diff --git tests/phpunit/tests/xmlrpc/basic.php tests/phpunit/tests/xmlrpc/basic.php
index bbbcbd7d5d..7818fdb0bf 100644
--- tests/phpunit/tests/xmlrpc/basic.php
+++ tests/phpunit/tests/xmlrpc/basic.php
@@ -11,7 +11,7 @@ class Tests_XMLRPC_Basic extends WP_XMLRPC_UnitTestCase {
 	function test_enabled() {
 		$result = $this->myxmlrpcserver->wp_getOptions( array( 1, 'username', 'password' ) );
 
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		// If disabled, 405 would result.
 		$this->assertEquals( 403, $result->code );
 	}
diff --git tests/phpunit/tests/xmlrpc/mt/getRecentPostTitles.php tests/phpunit/tests/xmlrpc/mt/getRecentPostTitles.php
index 8d9c027f22..7c36f978ef 100644
--- tests/phpunit/tests/xmlrpc/mt/getRecentPostTitles.php
+++ tests/phpunit/tests/xmlrpc/mt/getRecentPostTitles.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_mt_getRecentPostTitles extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->mt_getRecentPostTitles( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -15,7 +15,7 @@ class Tests_XMLRPC_mt_getRecentPostTitles extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'author' );
 
 		$result = $this->myxmlrpcserver->mt_getRecentPostTitles( array( 1, 'author', 'author' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 	}
 
@@ -25,7 +25,7 @@ class Tests_XMLRPC_mt_getRecentPostTitles extends WP_XMLRPC_UnitTestCase {
 		self::factory()->post->create( array( 'post_author' => $editor ) );
 
 		$result = $this->myxmlrpcserver->mt_getRecentPostTitles( array( 1, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( 0, count( $result ) );
 	}
 
@@ -35,7 +35,7 @@ class Tests_XMLRPC_mt_getRecentPostTitles extends WP_XMLRPC_UnitTestCase {
 		self::factory()->post->create();
 
 		$results = $this->myxmlrpcserver->mt_getRecentPostTitles( array( 1, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$post = get_post( $result['postid'] );
diff --git tests/phpunit/tests/xmlrpc/mw/editPost.php tests/phpunit/tests/xmlrpc/mw/editPost.php
index e265b8898f..39a937d7d5 100644
--- tests/phpunit/tests/xmlrpc/mw/editPost.php
+++ tests/phpunit/tests/xmlrpc/mw/editPost.php
@@ -8,7 +8,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 	function test_invalid_username_password() {
 		$post = array();
 		$result = $this->myxmlrpcserver->mw_editPost( array( 1, 'username', 'password', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -20,7 +20,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 		$new_title = 'Post test (updated)';
 		$post2 = array( 'title' => $new_title );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'contributor', 'contributor', $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -37,7 +37,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 		$new_title = 'Post test (updated)';
 		$post2 = array( 'title' => $new_title );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'editor', 'editor', $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -55,7 +55,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 		$new_title = 'Post test (updated)';
 		$post2 = array( 'title' => $new_title );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'contributor', 'contributor', $post2 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 
 		$out = get_post( $post_id );
@@ -72,7 +72,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'wp_author_id' => $author_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'editor', 'editor', $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -88,7 +88,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'wp_author_id' => $author_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'contributor', 'contributor', $post2 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 
 		$out = get_post( $post_id );
@@ -107,7 +107,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'wp_author_id' => $editor_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'editor', 'editor', $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -131,13 +131,13 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 		// add post thumbnail to post that does not have one
 		$post2 = array( 'wp_post_thumbnail' => $attachment_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'author', 'author', $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment_id, get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		// edit the post without supplying a post_thumbnail and check that it didn't change
 		$post3 = array( 'post_content' => 'Updated post' );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'author', 'author', $post3 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment_id, get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		// create another attachment
@@ -146,13 +146,13 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 		// change the post's post_thumbnail
 		$post4 = array( 'wp_post_thumbnail' => $attachment2_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'author', 'author', $post4 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment2_id, get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		// unset the post's post_thumbnail
 		$post5 = array( 'wp_post_thumbnail' => '' );
 		$result = $this->myxmlrpcserver->mw_editPost( array($post_id, 'author', 'author', $post5 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( '', get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		remove_theme_support( 'post-thumbnails' );
@@ -166,7 +166,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'title' => 'New Title', 'post_author' => $contributor_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'contributor', 'contributor', $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -174,7 +174,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post3 = array( 'description' => 'New Content', 'post_author' => $contributor_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'contributor', 'contributor', $post3 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -183,7 +183,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post4 = array( 'mt_excerpt' => 'New Excerpt', 'post_author' => $contributor_id );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'contributor', 'contributor', $post4 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -202,7 +202,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 		$post_id = wp_insert_post( $post );
 
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'editor', 'editor', array( 'sticky' => '1' ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue( $result );
 	}
 
@@ -215,7 +215,7 @@ class Tests_XMLRPC_mw_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'post_type' => 'page' );
 		$result = $this->myxmlrpcserver->mw_editPost( array( $post_id, 'contributor', 'contributor', $post2 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( $result->code, 401 );
 	}
 
diff --git tests/phpunit/tests/xmlrpc/mw/getPost.php tests/phpunit/tests/xmlrpc/mw/getPost.php
index 0d433d0804..924d6ff897 100644
--- tests/phpunit/tests/xmlrpc/mw/getPost.php
+++ tests/phpunit/tests/xmlrpc/mw/getPost.php
@@ -19,7 +19,7 @@ class Tests_XMLRPC_mw_getPost extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->mw_getPost( array( self::$post_id, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -27,7 +27,7 @@ class Tests_XMLRPC_mw_getPost extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->mw_getPost( array( self::$post_id, 'subscriber', 'subscriber' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -36,7 +36,7 @@ class Tests_XMLRPC_mw_getPost extends WP_XMLRPC_UnitTestCase {
 	 */
 	function test_invalid_postid() {
 		$result = $this->myxmlrpcserver->mw_getPost( array( 9999, 'author', 'author' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 	}
 
@@ -45,7 +45,7 @@ class Tests_XMLRPC_mw_getPost extends WP_XMLRPC_UnitTestCase {
 
 		$fields = array( 'post' );
 		$result = $this->myxmlrpcserver->mw_getPost( array( self::$post_id, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Check data types
 		$this->assertInternalType( 'string', $result['userid'] );
@@ -96,7 +96,7 @@ class Tests_XMLRPC_mw_getPost extends WP_XMLRPC_UnitTestCase {
 
 		$fields = array( 'post' );
 		$result = $this->myxmlrpcserver->mw_getPost( array( self::$post_id, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$this->assertInternalType( 'string', $result['wp_post_thumbnail'] );
 		$this->assertStringMatchesFormat( '%d', $result['wp_post_thumbnail'] );
@@ -108,7 +108,7 @@ class Tests_XMLRPC_mw_getPost extends WP_XMLRPC_UnitTestCase {
 	function test_date() {
 		$fields = array( 'post' );
 		$result = $this->myxmlrpcserver->mw_getPost( array( self::$post_id, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$this->assertInstanceOf( 'IXR_Date', $result['dateCreated'] );
 		$this->assertInstanceOf( 'IXR_Date', $result['date_created_gmt'] );
diff --git tests/phpunit/tests/xmlrpc/mw/getRecentPosts.php tests/phpunit/tests/xmlrpc/mw/getRecentPosts.php
index a3b7cd4074..8ab76274b4 100644
--- tests/phpunit/tests/xmlrpc/mw/getRecentPosts.php
+++ tests/phpunit/tests/xmlrpc/mw/getRecentPosts.php
@@ -20,7 +20,7 @@ class Tests_XMLRPC_mw_getRecentPosts extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->mw_getRecentPosts( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -31,7 +31,7 @@ class Tests_XMLRPC_mw_getRecentPosts extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->mw_getRecentPosts( array( 1, 'subscriber', 'subscriber' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -39,7 +39,7 @@ class Tests_XMLRPC_mw_getRecentPosts extends WP_XMLRPC_UnitTestCase {
 		wp_delete_post( self::$post_id, true );
 
 		$result = $this->myxmlrpcserver->mw_getRecentPosts( array( 1, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( 0, count( $result ) );
 	}
 
@@ -48,7 +48,7 @@ class Tests_XMLRPC_mw_getRecentPosts extends WP_XMLRPC_UnitTestCase {
 
 		$fields = array( 'post' );
 		$results = $this->myxmlrpcserver->mw_getRecentPosts( array( 1, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$post = get_post( $result['postid'] );
@@ -99,7 +99,7 @@ class Tests_XMLRPC_mw_getRecentPosts extends WP_XMLRPC_UnitTestCase {
 		set_post_thumbnail( self::$post_id, $attachment_id );
 
 		$results = $this->myxmlrpcserver->mw_getRecentPosts( array( self::$post_id, 'author', 'author' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$this->assertInternalType( 'string', $result['wp_post_thumbnail'] );
@@ -119,7 +119,7 @@ class Tests_XMLRPC_mw_getRecentPosts extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$results = $this->myxmlrpcserver->mw_getRecentPosts( array( 1, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$post = get_post( $result['postid'] );
diff --git tests/phpunit/tests/xmlrpc/mw/newPost.php tests/phpunit/tests/xmlrpc/mw/newPost.php
index 01316e62d5..06aaafc77f 100644
--- tests/phpunit/tests/xmlrpc/mw/newPost.php
+++ tests/phpunit/tests/xmlrpc/mw/newPost.php
@@ -8,7 +8,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 	function test_invalid_username_password() {
 		$post = array();
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'username', 'password', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -17,7 +17,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array();
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'subscriber', 'subscriber', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -26,7 +26,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array();
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 		$this->assertEquals( 'Content, title, and excerpt are empty.', $result->message );
 	}
@@ -36,7 +36,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test' );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 	}
 
@@ -45,7 +45,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'ID' => 103948 );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertNotEquals( '103948', $result );
 	}
 
@@ -54,7 +54,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'post_status' => 'publish' );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_incapable_publish() {
@@ -62,7 +62,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'post_status' => 'publish' );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'contributor', 'contributor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -72,7 +72,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'wp_author_id' => $other_author_id );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_incapable_other_author() {
@@ -81,7 +81,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'wp_author_id' => $other_author_id );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'contributor', 'contributor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -93,7 +93,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'wp_author_id' => 99999999 );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 	}
 
@@ -102,7 +102,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test' );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 
 		$out = get_post( $result );
@@ -121,7 +121,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Post Thumbnail Test', 'wp_post_thumbnail' => $attachment_id );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment_id, get_post_meta( $result, '_thumbnail_id', true ) );
 
 		remove_theme_support( 'post-thumbnails' );
@@ -132,7 +132,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'post_type' => 'page' );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -141,7 +141,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'title' => 'Test', 'post_type' => 'page' );
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 
 		$out = get_post( $result );
@@ -162,7 +162,7 @@ class Tests_XMLRPC_mw_newPost extends WP_XMLRPC_UnitTestCase {
 			'post_status' => 'draft'
 		);
 		$result = $this->myxmlrpcserver->mw_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 
 		$out = get_post( $result );
diff --git tests/phpunit/tests/xmlrpc/wp/deletePost.php tests/phpunit/tests/xmlrpc/wp/deletePost.php
index e7284a7cde..d2a5bc6460 100644
--- tests/phpunit/tests/xmlrpc/wp/deletePost.php
+++ tests/phpunit/tests/xmlrpc/wp/deletePost.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_deletePost extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_deletePost( array( 1, 'username', 'password', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -15,7 +15,7 @@ class Tests_XMLRPC_wp_deletePost extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_deletePost( array( 1, 'editor', 'editor', 340982340 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 	}
 
@@ -24,7 +24,7 @@ class Tests_XMLRPC_wp_deletePost extends WP_XMLRPC_UnitTestCase {
 		$post_id = self::factory()->post->create();
 
 		$result = $this->myxmlrpcserver->wp_deletePost( array( 1, 'subscriber', 'subscriber', $post_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -33,7 +33,7 @@ class Tests_XMLRPC_wp_deletePost extends WP_XMLRPC_UnitTestCase {
 		$post_id = self::factory()->post->create();
 
 		$result = $this->myxmlrpcserver->wp_deletePost( array( 1, 'editor', 'editor', $post_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue( $result );
 
 		$post = get_post( $post_id );
diff --git tests/phpunit/tests/xmlrpc/wp/deleteTerm.php tests/phpunit/tests/xmlrpc/wp/deleteTerm.php
index ee95c6ae76..94e25c9c3d 100644
--- tests/phpunit/tests/xmlrpc/wp/deleteTerm.php
+++ tests/phpunit/tests/xmlrpc/wp/deleteTerm.php
@@ -14,7 +14,7 @@ class Tests_XMLRPC_wp_deleteTerm extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_deleteTerm( array( 1, 'username', 'password', 'category', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -22,7 +22,7 @@ class Tests_XMLRPC_wp_deleteTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_deleteTerm( array( 1, 'subscriber', 'subscriber', '', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -31,7 +31,7 @@ class Tests_XMLRPC_wp_deleteTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_deleteTerm( array( 1, 'subscriber', 'subscriber', 'not_existing', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -40,7 +40,7 @@ class Tests_XMLRPC_wp_deleteTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_deleteTerm( array( 1, 'subscriber', 'subscriber', 'category', self::$term_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 		$this->assertEquals( __( 'Sorry, you are not allowed to delete this term.' ), $result->message );
 	}
@@ -49,7 +49,7 @@ class Tests_XMLRPC_wp_deleteTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_deleteTerm( array( 1, 'editor', 'editor', 'category', '' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 		$this->assertEquals( __('Empty Term'), $result->message );
 	}
@@ -58,7 +58,7 @@ class Tests_XMLRPC_wp_deleteTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_deleteTerm( array( 1, 'editor', 'editor', 'category', 9999 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 		$this->assertEquals( __( 'Invalid term ID.' ), $result->message );
 	}
@@ -67,7 +67,7 @@ class Tests_XMLRPC_wp_deleteTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_deleteTerm( array( 1, 'editor', 'editor', 'category', self::$term_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertInternalType( 'boolean', $result );
 	}
 }
diff --git tests/phpunit/tests/xmlrpc/wp/editComment.php tests/phpunit/tests/xmlrpc/wp/editComment.php
index b43beb6ee0..fcb3bb57f7 100644
--- tests/phpunit/tests/xmlrpc/wp/editComment.php
+++ tests/phpunit/tests/xmlrpc/wp/editComment.php
@@ -22,7 +22,7 @@ class Tests_XMLRPC_wp_editComment extends WP_XMLRPC_UnitTestCase {
 		$result = $this->myxmlrpcserver->wp_editComment( array( 1, 'author', 'author', $comment_id, array(
 			'status' => 'hold'
 		) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue( $result );
 	}
 
@@ -42,7 +42,7 @@ class Tests_XMLRPC_wp_editComment extends WP_XMLRPC_UnitTestCase {
 		) );
 
 		$result = $this->myxmlrpcserver->wp_editComment( array( 1, 'author', 'author', $comment_id, array( 'status' => 'hold' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Sorry, you are not allowed to moderate or edit this comment.' ), $result->message );
 	}
diff --git tests/phpunit/tests/xmlrpc/wp/editPost.php tests/phpunit/tests/xmlrpc/wp/editPost.php
index 373d45870a..55f5be99a7 100644
--- tests/phpunit/tests/xmlrpc/wp/editPost.php
+++ tests/phpunit/tests/xmlrpc/wp/editPost.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'username', 'password', 0, array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -20,7 +20,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		$new_title = 'Post test (updated)';
 		$post2 = array( 'post_title' => $new_title );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'contributor', 'contributor', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -37,7 +37,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		$new_title = 'Post test (updated)';
 		$post2 = array( 'post_title' => $new_title );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -55,7 +55,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		$new_title = 'Post test (updated)';
 		$post2 = array( 'post_title' => $new_title );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'contributor', 'contributor', $post_id, $post2 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 
 		$out = get_post( $post_id );
@@ -72,7 +72,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'post_author' => $author_id );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -88,7 +88,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'post_author' => $author_id );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'contributor', 'contributor', $post_id, $post2 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 
 		$out = get_post( $post_id );
@@ -107,7 +107,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'post_author' => $editor_id );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -131,12 +131,12 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		// add post thumbnail to post that does not have one
 		$post2 = array( 'post_thumbnail' => $attachment_id );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'author', 'author', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment_id, get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		// fetch the post to verify that it appears
 		$result = $this->myxmlrpcserver->wp_getPost( array( 1, 'author', 'author', $post_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertArrayHasKey( 'post_thumbnail', $result );
 		$this->assertInternalType( 'array', $result['post_thumbnail'] );
 		$this->assertEquals( $attachment_id, $result['post_thumbnail']['attachment_id'] );
@@ -144,7 +144,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		// edit the post without supplying a post_thumbnail and check that it didn't change
 		$post3 = array( 'post_content' => 'Updated post' );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'author', 'author', $post_id, $post3 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment_id, get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		// create another attachment
@@ -153,19 +153,19 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		// change the post's post_thumbnail
 		$post4 = array( 'post_thumbnail' => $attachment2_id );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'author', 'author', $post_id, $post4 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment2_id, get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		// unset the post's post_thumbnail
 		$post5 = array( 'post_thumbnail' => '' );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'author', 'author', $post_id, $post5 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( '', get_post_meta( $post_id, '_thumbnail_id', true ) );
 
 		// use invalid ID
 		$post6 = array( 'post_thumbnail' => 398420983409 );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'author', 'author', $post_id, $post6 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 
 		remove_theme_support( 'post-thumbnails' );
@@ -191,7 +191,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		);
 
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'contributor', 'contributor', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue($result);
 
 		$out = get_post( $post_id );
@@ -213,7 +213,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'sticky' => false );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertFalse( is_sticky( $post_id ) );
 	}
 
@@ -225,7 +225,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$post2 = array( 'post_password' => 'foobar',  'sticky' => false );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $post2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertFalse( is_sticky( $post_id ) );
 	}
 
@@ -245,7 +245,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		// Modify the day old post. In this case, we think it was last modified yesterday.
 		$struct = array( 'post_content' => 'First edit', 'if_not_modified_since' => new IXR_Date( $yesterday ) );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $struct ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Make sure the edit went through.
 		$this->assertEquals( 'First edit', get_post( $post_id )->post_content );
@@ -253,7 +253,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		// Modify it again. We think it was last modified yesterday, but we actually just modified it above.
 		$struct = array( 'post_content' => 'Second edit', 'if_not_modified_since' => new IXR_Date( $yesterday ) );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $struct ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 409, $result->code );
 
 		// Make sure the edit did not go through.
@@ -273,7 +273,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$struct = array( 'post_content' => 'First edit' );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $struct ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Make sure that the post status is still inherit
 		$this->assertEquals( 'inherit', get_post( $post_id )->post_status );
@@ -290,7 +290,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 
 		$struct = array( 'post_status' => 'doesnt_exists' );
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $struct ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Make sure that the post status is still inherit
 		$this->assertEquals( 'draft', get_post( $post_id )->post_status );
@@ -309,7 +309,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 		$this->assertContains( $term_id, $term_ids );
 
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, array( 'ID' => $post_id, 'post_title' => 'Updated' ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( 'Updated', get_post( $post_id )->post_title );
 
 		$term_ids = wp_list_pluck( get_the_category( $post_id ), 'term_id' );
@@ -336,7 +336,7 @@ class Tests_XMLRPC_wp_editPost extends WP_XMLRPC_UnitTestCase {
 			)
 		);
 		$result = $this->myxmlrpcserver->wp_editPost( array( 1, 'editor', 'editor', $post_id, $new_post_content ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( 'Updated', get_post( $post_id )->post_title );
 
 		$term_ids = wp_list_pluck( get_the_category( $post_id ), 'term_id' );
diff --git tests/phpunit/tests/xmlrpc/wp/editProfile.php tests/phpunit/tests/xmlrpc/wp/editProfile.php
index 525f6a5652..6e3ced529a 100644
--- tests/phpunit/tests/xmlrpc/wp/editProfile.php
+++ tests/phpunit/tests/xmlrpc/wp/editProfile.php
@@ -8,7 +8,7 @@ class Tests_XMLRPC_wp_editProfile extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_editProfile( array( 1, 'username', 'password', array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -25,7 +25,7 @@ class Tests_XMLRPC_wp_editProfile extends WP_XMLRPC_UnitTestCase {
             'bio' => rand_str(200)
         );
         $result = $this->myxmlrpcserver->wp_editProfile( array( 1, 'subscriber', 'subscriber', $new_data ) );
-        $this->assertNotInstanceOf( 'IXR_Error', $result );
+        $this->assertNotIXRError( $result );
         $this->assertTrue( $result );
 
         // verify that the new values were stored
@@ -45,7 +45,7 @@ class Tests_XMLRPC_wp_editProfile extends WP_XMLRPC_UnitTestCase {
         $new_data = array( 'password' => $new_pass );
 
         $result = $this->myxmlrpcserver->wp_editProfile( array( 1, 'author', 'author', $new_data ) );
-        $this->assertNotInstanceOf( 'IXR_Error', $result );
+        $this->assertNotIXRError( $result );
         $this->assertTrue( $result );
 
         $auth_old = wp_authenticate( 'author', 'author' );
@@ -60,7 +60,7 @@ class Tests_XMLRPC_wp_editProfile extends WP_XMLRPC_UnitTestCase {
         $new_data = array( 'email' => $new_email );
 
         $result = $this->myxmlrpcserver->wp_editProfile( array( 1, 'editor', 'editor', $new_data ) );
-        $this->assertNotInstanceOf( 'IXR_Error', $result );
+        $this->assertNotIXRError( $result );
         $this->assertTrue( $result );
 
         $user_data = get_userdata( $editor_id );
diff --git tests/phpunit/tests/xmlrpc/wp/editTerm.php tests/phpunit/tests/xmlrpc/wp/editTerm.php
index b3f22d2a24..1e62de9d1f 100644
--- tests/phpunit/tests/xmlrpc/wp/editTerm.php
+++ tests/phpunit/tests/xmlrpc/wp/editTerm.php
@@ -22,7 +22,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'username', 'password', 'category', 1 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -30,7 +30,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'subscriber', 'subscriber', '', array( 'taxonomy' => '' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -39,7 +39,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'subscriber', 'subscriber', self::$parent_term, array( 'taxonomy' => 'not_existing' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -48,7 +48,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'subscriber', 'subscriber', self::$parent_term, array( 'taxonomy' => 'category' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 		$this->assertEquals( __( 'Sorry, you are not allowed to edit this term.' ), $result->message );
 	}
@@ -57,7 +57,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', 9999, array( 'taxonomy' => 'category' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 		$this->assertEquals(  __( 'Invalid term ID.' ), $result->message );
 	}
@@ -66,7 +66,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', '', array( 'taxonomy' => 'category' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 		$this->assertEquals( __('Empty Term'), $result->message );
 	}
@@ -75,7 +75,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$parent_term, array( 'taxonomy' => 'category', 'name' => '' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'The term name cannot be empty.' ), $result->message );
 	}
@@ -84,7 +84,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$post_tag, array( 'taxonomy' => 'post_tag', 'parent' => self::$parent_term ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( "This taxonomy is not hierarchical so you can't set a parent." ), $result->message );
 	}
@@ -93,7 +93,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$child_term, array( 'taxonomy' => 'category', 'parent' => '', 'name' => 'test' ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue( $result );
 	}
 
@@ -102,7 +102,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$child_term, array( 'taxonomy' => 'category', 'parent' => NULL, 'name' => 'test' ) ) );
 
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertInternalType( 'boolean', $result );
 
 		$term = get_term( self::$child_term, 'category' );
@@ -113,7 +113,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$child_term, array( 'taxonomy' => 'category', 'parent' => 'dasda', 'name' => 'test' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 	}
 
@@ -121,7 +121,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$child_term, array( 'taxonomy' => 'category', 'parent' => 9999, 'name' => 'test' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Parent term does not exist.' ), $result->message );
 	}
@@ -131,7 +131,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 
 		$parent_term = get_term_by( 'id', self::$parent_term, 'category' );
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$child_term, array( 'taxonomy' => 'category', 'slug' => $parent_term->slug ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 		$this->assertEquals( htmlspecialchars( sprintf( __('The slug &#8220;%s&#8221; is already in use by another term'), $parent_term->slug ) ), $result->message );
 	}
@@ -142,7 +142,7 @@ class Tests_XMLRPC_wp_editTerm extends WP_XMLRPC_UnitTestCase {
 		$fields = array( 'taxonomy' => 'category', 'name' => 'Child 2', 'parent' => self::$parent_term, 'description' => 'Child term', 'slug' => 'child_2' );
 		$result = $this->myxmlrpcserver->wp_editTerm( array( 1, 'editor', 'editor', self::$child_term, $fields ) );
 
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertInternalType( 'boolean', $result );
 	}
 }
diff --git tests/phpunit/tests/xmlrpc/wp/getComment.php tests/phpunit/tests/xmlrpc/wp/getComment.php
index d66ccd8a0e..57ad8995f1 100644
--- tests/phpunit/tests/xmlrpc/wp/getComment.php
+++ tests/phpunit/tests/xmlrpc/wp/getComment.php
@@ -35,7 +35,7 @@ class Tests_XMLRPC_wp_getComment extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getComment( array( 1, 'username', 'password', self::$parent_comment_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -43,7 +43,7 @@ class Tests_XMLRPC_wp_getComment extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'contributor' );
 
 		$result = $this->myxmlrpcserver->wp_getComment( array( 1, 'contributor', 'contributor', self::$parent_comment_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -51,7 +51,7 @@ class Tests_XMLRPC_wp_getComment extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getComment( array( 1, 'editor', 'editor', self::$parent_comment_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Check data types
 		$this->assertInternalType( 'string', $result['user_id'] );
@@ -87,7 +87,7 @@ class Tests_XMLRPC_wp_getComment extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getComment( array( 1, 'editor', 'editor', self::$child_comment_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$this->assertEquals( self::$child_comment_id, $result['comment_id'] );
 		$this->assertEquals( self::$parent_comment_id, $result['parent'] );
@@ -97,7 +97,7 @@ class Tests_XMLRPC_wp_getComment extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getComment( array( 1, 'editor', 'editor', 123456789 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 	}
 }
\ No newline at end of file
diff --git tests/phpunit/tests/xmlrpc/wp/getComments.php tests/phpunit/tests/xmlrpc/wp/getComments.php
index a4bdf22333..49b72535b7 100644
--- tests/phpunit/tests/xmlrpc/wp/getComments.php
+++ tests/phpunit/tests/xmlrpc/wp/getComments.php
@@ -8,7 +8,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getComments( array( 1, 'username', 'password', array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -16,7 +16,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'contributor' );
 
 		$result = $this->myxmlrpcserver->wp_getComments( array( 1, 'contributor', 'contributor', array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -27,7 +27,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$results = $this->myxmlrpcserver->wp_getComments( array( 1, 'editor', 'editor', array() ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$comment = get_comment( $result['comment_id'], ARRAY_A );
@@ -44,7 +44,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 		$results = $this->myxmlrpcserver->wp_getComments( array( 1, 'editor', 'editor', array(
 			'post_id' => $this->post_id
 		) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$this->assertEquals( $this->post_id, $result['post_id'] );
@@ -60,7 +60,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 		$results = $this->myxmlrpcserver->wp_getComments( array( 1, 'editor', 'editor', array(
 			'post_id' => $this->post_id,
 		) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		// if no 'number' filter is specified, default should be 10
 		$this->assertCount( 10, $results );
@@ -69,7 +69,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 			'post_id' => $this->post_id,
 			'number' => 5
 		) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results2 );
+		$this->assertNotIXRError( $results2 );
 		$this->assertCount( 5, $results2 );
 	}
 
@@ -104,7 +104,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 		) );
 
 		$result = $this->myxmlrpcserver->wp_getComments( array( 1, 'contributor', 'contributor' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -140,7 +140,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 		$result1 = $this->myxmlrpcserver->wp_getComments( array( 1, 'author', 'author', array(
 			'post_id' => $author_post_id
 		) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result1 );
+		$this->assertIXRError( $result1 );
 
 		$result2 = $this->myxmlrpcserver->wp_getComments( array( 1, 'author', 'author', array(
 			'status' => 'approve',
@@ -153,7 +153,7 @@ class Tests_XMLRPC_wp_getComments extends WP_XMLRPC_UnitTestCase {
 		$result3 = $this->myxmlrpcserver->wp_getComments( array( 1, 'author', 'author', array(
 			'post_id' => $editor_post_id
 		) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result3 );
+		$this->assertIXRError( $result3 );
 
 		$result4 = $this->myxmlrpcserver->wp_getComments( array( 1, 'author', 'author', array(
 			'status' => 'approve',
diff --git tests/phpunit/tests/xmlrpc/wp/getMediaItem.php tests/phpunit/tests/xmlrpc/wp/getMediaItem.php
index 7b99dd5a04..a091f1c2b6 100644
--- tests/phpunit/tests/xmlrpc/wp/getMediaItem.php
+++ tests/phpunit/tests/xmlrpc/wp/getMediaItem.php
@@ -38,7 +38,7 @@ class Tests_XMLRPC_wp_getMediaItem extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getMediaItem( array( 1, 'username', 'password', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -47,7 +47,7 @@ class Tests_XMLRPC_wp_getMediaItem extends WP_XMLRPC_UnitTestCase {
 
 		$fields = array( 'post' );
 		$result = $this->myxmlrpcserver->wp_getMediaItem( array( 1, 'author', 'author', $this->attachment_id, $fields ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Check data types
 		$this->assertInternalType( 'string', $result['attachment_id'] );
diff --git tests/phpunit/tests/xmlrpc/wp/getOptions.php tests/phpunit/tests/xmlrpc/wp/getOptions.php
index 8b095f65c5..0dffcff231 100644
--- tests/phpunit/tests/xmlrpc/wp/getOptions.php
+++ tests/phpunit/tests/xmlrpc/wp/getOptions.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_getOptions extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getOptions( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
diff --git tests/phpunit/tests/xmlrpc/wp/getPage.php tests/phpunit/tests/xmlrpc/wp/getPage.php
index 0f377b13b8..eb57239c95 100644
--- tests/phpunit/tests/xmlrpc/wp/getPage.php
+++ tests/phpunit/tests/xmlrpc/wp/getPage.php
@@ -20,7 +20,7 @@ class Tests_XMLRPC_wp_getPage extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getPage( array( 1, self::$post_id, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -31,7 +31,7 @@ class Tests_XMLRPC_wp_getPage extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPage( array( 1, 9999, 'editor', 'editor' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 	}
 
@@ -39,7 +39,7 @@ class Tests_XMLRPC_wp_getPage extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPage( array( 1, self::$post_id, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Check data types
 		$this->assertInternalType( 'string', $result['userid'] );
@@ -80,7 +80,7 @@ class Tests_XMLRPC_wp_getPage extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPage( array( 1, self::$post_id, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$this->assertInstanceOf( 'IXR_Date', $result['dateCreated'] );
 		$this->assertInstanceOf( 'IXR_Date', $result['date_created_gmt'] );
diff --git tests/phpunit/tests/xmlrpc/wp/getPageList.php tests/phpunit/tests/xmlrpc/wp/getPageList.php
index ef8f793ca1..0e924c4ef4 100644
--- tests/phpunit/tests/xmlrpc/wp/getPageList.php
+++ tests/phpunit/tests/xmlrpc/wp/getPageList.php
@@ -20,7 +20,7 @@ class Tests_XMLRPC_wp_getPageList extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getPageList( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -28,7 +28,7 @@ class Tests_XMLRPC_wp_getPageList extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'contributor' );
 
 		$result = $this->myxmlrpcserver->wp_getPageList( array( 1, 'contributor', 'contributor' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -36,7 +36,7 @@ class Tests_XMLRPC_wp_getPageList extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$results = $this->myxmlrpcserver->wp_getPageList( array( 1, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$page = get_post( $result->page_id );
diff --git tests/phpunit/tests/xmlrpc/wp/getPages.php tests/phpunit/tests/xmlrpc/wp/getPages.php
index 424238794a..f528d832ff 100644
--- tests/phpunit/tests/xmlrpc/wp/getPages.php
+++ tests/phpunit/tests/xmlrpc/wp/getPages.php
@@ -26,7 +26,7 @@ class Tests_XMLRPC_wp_getPages extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getPages( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -34,13 +34,13 @@ class Tests_XMLRPC_wp_getPages extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'contributor' );
 
 		$result = $this->myxmlrpcserver->wp_getPages( array( 1, 'contributor', 'contributor' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
 	function test_capable_user() {
 		$results = $this->myxmlrpcserver->wp_getPages( array( 1, 'administrator', 'administrator' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $result ) {
 			$page = get_post( $result['page_id'] );
@@ -65,12 +65,12 @@ class Tests_XMLRPC_wp_getPages extends WP_XMLRPC_UnitTestCase {
 		add_filter( 'map_meta_cap', array( $this, 'remove_editor_edit_page_cap') , 10, 4 );
 
 		$results = $this->myxmlrpcserver->wp_getPages( array( 1, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		$found_incapable = false;
 		foreach( $results as $result ) {
 			// WP#20629
-			$this->assertNotInstanceOf( 'IXR_Error', $result );
+			$this->assertNotIXRError( $result );
 
 			if ( $result['page_id'] == self::$post_id ) {
 				$found_incapable = true;
diff --git tests/phpunit/tests/xmlrpc/wp/getPost.php tests/phpunit/tests/xmlrpc/wp/getPost.php
index 6e6ecaeae9..b33f8a3021 100644
--- tests/phpunit/tests/xmlrpc/wp/getPost.php
+++ tests/phpunit/tests/xmlrpc/wp/getPost.php
@@ -27,7 +27,7 @@ class Tests_XMLRPC_wp_getPost extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getPost( array( 1, 'username', 'password', 1 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -36,7 +36,7 @@ class Tests_XMLRPC_wp_getPost extends WP_XMLRPC_UnitTestCase {
 
 		$fields = array( 'post', 'custom_fields' );
 		$result = $this->myxmlrpcserver->wp_getPost( array( 1, 'author', 'author', $this->post_id, $fields ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Check data types
 		$this->assertInternalType( 'string', $result['post_id'] );
@@ -79,7 +79,7 @@ class Tests_XMLRPC_wp_getPost extends WP_XMLRPC_UnitTestCase {
 	function test_no_fields() {
 		$fields = array();
 		$result = $this->myxmlrpcserver->wp_getPost( array( 1, 'author', 'author', $this->post_id, $fields ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// when no fields are requested, only the IDs should be returned
 		$this->assertEquals( 1, count( $result ) );
@@ -88,7 +88,7 @@ class Tests_XMLRPC_wp_getPost extends WP_XMLRPC_UnitTestCase {
 
 	function test_default_fields() {
 		$result = $this->myxmlrpcserver->wp_getPost( array( 1, 'author', 'author', $this->post_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$this->assertArrayHasKey( 'post_id', $result );
 		$this->assertArrayHasKey( 'link', $result ); // random field from 'posts' group
@@ -99,7 +99,7 @@ class Tests_XMLRPC_wp_getPost extends WP_XMLRPC_UnitTestCase {
 	function test_date() {
 		$fields = array( 'post' );
 		$result = $this->myxmlrpcserver->wp_getPost( array( 1, 'author', 'author', $this->post_id, $fields ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$this->assertInstanceOf( 'IXR_Date', $result['post_date'] );
 		$this->assertInstanceOf( 'IXR_Date', $result['post_date_gmt'] );
@@ -130,7 +130,7 @@ class Tests_XMLRPC_wp_getPost extends WP_XMLRPC_UnitTestCase {
 		) );
 
 		$result = $this->myxmlrpcserver->wp_getPost( array( 1, 'editor', 'editor', $child_page_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$this->assertInternalType( 'string', $result['post_id'] );
 		$this->assertInternalType( 'string', $result['post_parent'] );
diff --git tests/phpunit/tests/xmlrpc/wp/getPostType.php tests/phpunit/tests/xmlrpc/wp/getPostType.php
index a00dbda3f7..cef0fd6981 100644
--- tests/phpunit/tests/xmlrpc/wp/getPostType.php
+++ tests/phpunit/tests/xmlrpc/wp/getPostType.php
@@ -31,7 +31,7 @@ class Tests_XMLRPC_wp_getPostType extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getPostType( array( 1, 'username', 'password', 'post' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -39,7 +39,7 @@ class Tests_XMLRPC_wp_getPostType extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPostType( array( 1, 'editor', 'editor', 'foobar' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -47,14 +47,14 @@ class Tests_XMLRPC_wp_getPostType extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPostType( array( 1, 'editor', 'editor', 'post' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_incapable_user() {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getPostType( array( 1, 'subscriber', 'subscriber', 'post' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -62,7 +62,7 @@ class Tests_XMLRPC_wp_getPostType extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPostType( array( 1, 'editor', 'editor', $this->cpt_name, array( 'labels', 'cap', 'menu', 'taxonomies' ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// check data types
 		$this->assertInternalType( 'string', $result['name'] );
diff --git tests/phpunit/tests/xmlrpc/wp/getPostTypes.php tests/phpunit/tests/xmlrpc/wp/getPostTypes.php
index ae78a5db51..7188411931 100644
--- tests/phpunit/tests/xmlrpc/wp/getPostTypes.php
+++ tests/phpunit/tests/xmlrpc/wp/getPostTypes.php
@@ -6,7 +6,7 @@
 class Tests_XMLRPC_wp_getPostTypes extends WP_XMLRPC_UnitTestCase {
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getPostTypes( array( 1, 'username', 'password', 'post' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -14,7 +14,7 @@ class Tests_XMLRPC_wp_getPostTypes extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getPostTypes( array( 1, 'subscriber', 'subscriber' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertInternalType( 'array', $result );
 		$this->assertEquals( 0, count( $result ) );
 	}
@@ -23,7 +23,7 @@ class Tests_XMLRPC_wp_getPostTypes extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPostTypes( array( 1, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertInternalType( 'array', $result );
 		$this->assertGreaterThan( 0, count( $result ) );
 	}
@@ -32,7 +32,7 @@ class Tests_XMLRPC_wp_getPostTypes extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPostTypes( array( 1, 'editor', 'editor', array( 'hierarchical' => true ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertInternalType( 'array', $result );
 
 		// verify that pages is in the result, and post is not
diff --git tests/phpunit/tests/xmlrpc/wp/getPosts.php tests/phpunit/tests/xmlrpc/wp/getPosts.php
index 3119fea61f..28d3c4b28d 100644
--- tests/phpunit/tests/xmlrpc/wp/getPosts.php
+++ tests/phpunit/tests/xmlrpc/wp/getPosts.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getPosts( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -18,12 +18,12 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getPosts( array( 1, 'subscriber', 'subscriber' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 
 		$filter = array( 'post_type' => 'page' );
 		$result = $this->myxmlrpcserver->wp_getPosts( array( 1, 'subscriber', 'subscriber', $filter ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -31,7 +31,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_invalid_post_type() {
@@ -39,7 +39,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 
 		$filter = array( 'post_type' => 'invalid_post_type_name' );
 		$result = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor', $filter ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 	}
 
 	function test_filters() {
@@ -62,7 +62,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 		// get them all
 		$filter = array( 'post_type' => $cpt_name, 'number' => $num_posts + 10 );
 		$results = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$this->assertEquals( $num_posts, count( $results ) );
 
 		// page through results
@@ -86,7 +86,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 		// get results ordered by comment count
 		$filter2 = array( 'post_type' => $cpt_name, 'number' => $num_posts, 'orderby' => 'comment_count', 'order' => 'DESC' );
 		$results2 = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor', $filter2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results2 );
+		$this->assertNotIXRError( $results2 );
 		$last_comment_count = 100;
 		foreach ( $results2 as $post ) {
 			$comment_count = intval( get_comments_number( $post['post_id'] ) );
@@ -100,7 +100,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 		wp_update_post( $post );
 		$filter3 = array( 'post_type' => $cpt_name, 'post_status' => 'draft' );
 		$results3 = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor', $filter3 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results3 );
+		$this->assertNotIXRError( $results3 );
 		$this->assertEquals( 1, count( $results3 ) );
 		$this->assertEquals( $post->ID, $results3[0]['post_id'] );
 
@@ -113,7 +113,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 
 		// check default fields
 		$results = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$expected_fields = array( 'post_id', 'post_title', 'terms', 'custom_fields', 'link' ); // subset of expected fields
 		foreach( $expected_fields as $field ) {
 			$this->assertArrayHasKey( $field, $results[0] );
@@ -123,7 +123,7 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 		$filter = array();
 		$fields = array( 'post_name', 'post_author', 'enclosure' );
 		$results2 = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor', $filter, $fields ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results2 );
+		$this->assertNotIXRError( $results2 );
 		$expected_fields = array_merge( $fields, array( 'post_id' ) );
 		foreach ( array_keys( $results2[0] ) as $field ) {
 			$this->assertContains( $field, $expected_fields );
@@ -142,13 +142,13 @@ class Tests_XMLRPC_wp_getPosts extends WP_XMLRPC_UnitTestCase {
 		// Search for none of them
 		$filter = array( 's' => 'Third' );
 		$results = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$this->assertEquals( 0, count( $results ) );
 
 		// Search for one of them
 		$filter = array( 's' => 'First:' );
 		$results = $this->myxmlrpcserver->wp_getPosts( array( 1, 'editor', 'editor', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$this->assertEquals( 1, count( $results ) );
 	}
 
diff --git tests/phpunit/tests/xmlrpc/wp/getProfile.php tests/phpunit/tests/xmlrpc/wp/getProfile.php
index cc2da3e46a..86fd8213dd 100644
--- tests/phpunit/tests/xmlrpc/wp/getProfile.php
+++ tests/phpunit/tests/xmlrpc/wp/getProfile.php
@@ -8,7 +8,7 @@ class Tests_XMLRPC_wp_getProfile extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getProfile( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -16,7 +16,7 @@ class Tests_XMLRPC_wp_getProfile extends WP_XMLRPC_UnitTestCase {
 		$subscriber_id = $this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getProfile( array( 1, 'subscriber', 'subscriber' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $subscriber_id, $result['user_id'] );
 		$this->assertContains( 'subscriber', $result['roles'] );
 	}
@@ -25,7 +25,7 @@ class Tests_XMLRPC_wp_getProfile extends WP_XMLRPC_UnitTestCase {
 		$administrator_id = $this->make_user_by_role( 'administrator' );
 
 		$result = $this->myxmlrpcserver->wp_getProfile( array( 1, 'administrator', 'administrator' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $administrator_id, $result['user_id'] );
 		$this->assertContains( 'administrator', $result['roles'] );
 	}
@@ -36,7 +36,7 @@ class Tests_XMLRPC_wp_getProfile extends WP_XMLRPC_UnitTestCase {
 		$fields = array( 'email', 'bio', 'user_contacts' );
 
 		$result = $this->myxmlrpcserver->wp_getProfile( array( 1, 'editor', 'editor', $fields ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $editor_id, $result['user_id'] );
 
 		$expected_fields = array( 'user_id', 'email', 'bio' );
diff --git tests/phpunit/tests/xmlrpc/wp/getRevisions.php tests/phpunit/tests/xmlrpc/wp/getRevisions.php
index a407c65ae2..d1aad1e390 100644
--- tests/phpunit/tests/xmlrpc/wp/getRevisions.php
+++ tests/phpunit/tests/xmlrpc/wp/getRevisions.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_getRevisions extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getRevisions( array( 1, 'username', 'password', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -17,7 +17,7 @@ class Tests_XMLRPC_wp_getRevisions extends WP_XMLRPC_UnitTestCase {
 		$post_id = self::factory()->post->create();
 
 		$result = $this->myxmlrpcserver->wp_getRevisions( array( 1, 'subscriber', 'subscriber', $post_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -26,7 +26,7 @@ class Tests_XMLRPC_wp_getRevisions extends WP_XMLRPC_UnitTestCase {
 
 		$post_id = self::factory()->post->create();
 		$result = $this->myxmlrpcserver->wp_getRevisions( array( 1, 'editor', 'editor', $post_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_revision_count() {
diff --git tests/phpunit/tests/xmlrpc/wp/getTaxonomies.php tests/phpunit/tests/xmlrpc/wp/getTaxonomies.php
index cd2c86e3cc..97bd9cf467 100644
--- tests/phpunit/tests/xmlrpc/wp/getTaxonomies.php
+++ tests/phpunit/tests/xmlrpc/wp/getTaxonomies.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_getTaxonomies extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getTaxonomies( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -15,6 +15,6 @@ class Tests_XMLRPC_wp_getTaxonomies extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTaxonomies( array( 1, 'editor', 'editor' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 }
\ No newline at end of file
diff --git tests/phpunit/tests/xmlrpc/wp/getTaxonomy.php tests/phpunit/tests/xmlrpc/wp/getTaxonomy.php
index f8446bcbf9..5ffff80a81 100644
--- tests/phpunit/tests/xmlrpc/wp/getTaxonomy.php
+++ tests/phpunit/tests/xmlrpc/wp/getTaxonomy.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_getTaxonomy extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getTaxonomy( array( 1, 'username', 'password', 'category' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -15,7 +15,7 @@ class Tests_XMLRPC_wp_getTaxonomy extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTaxonomy( array( 1, 'editor', 'editor', '' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -24,7 +24,7 @@ class Tests_XMLRPC_wp_getTaxonomy extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTaxonomy( array( 1, 'editor', 'editor', 'not_existing' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -33,7 +33,7 @@ class Tests_XMLRPC_wp_getTaxonomy extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getTaxonomy( array( 1, 'subscriber', 'subscriber', 'category' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 		$this->assertEquals( __( 'Sorry, you are not allowed to assign terms in this taxonomy.' ), $result->message );
 	}
@@ -42,14 +42,14 @@ class Tests_XMLRPC_wp_getTaxonomy extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTaxonomy( array( 1, 'editor', 'editor', 'category' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_prepare_taxonomy() {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTaxonomy( array( 1, 'editor', 'editor', 'category' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$taxonomy = get_taxonomy( 'category' );
 		$this->assertEquals( 'category', $result['name'], 'name' );
 		$this->assertEquals( true, $result['_builtin'], '_builtin' );
diff --git tests/phpunit/tests/xmlrpc/wp/getTerm.php tests/phpunit/tests/xmlrpc/wp/getTerm.php
index 2edbaeb2ff..fca71a7a95 100644
--- tests/phpunit/tests/xmlrpc/wp/getTerm.php
+++ tests/phpunit/tests/xmlrpc/wp/getTerm.php
@@ -15,7 +15,7 @@ class Tests_XMLRPC_wp_getTerm extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getTerm( array( 1, 'username', 'password', 'category', 1 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -23,7 +23,7 @@ class Tests_XMLRPC_wp_getTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTerm( array( 1, 'editor', 'editor', '', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -32,7 +32,7 @@ class Tests_XMLRPC_wp_getTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTerm( array( 1, 'editor', 'editor', 'not_existing', 0 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -41,7 +41,7 @@ class Tests_XMLRPC_wp_getTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getTerm( array( 1, 'subscriber', 'subscriber', 'category', self::$term_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 		$this->assertEquals( __( 'Sorry, you are not allowed to assign this term.' ), $result->message );
 	}
@@ -51,7 +51,7 @@ class Tests_XMLRPC_wp_getTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTerm( array( 1, 'editor', 'editor', 'category', '' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 		$this->assertEquals( __('Empty Term'), $result->message );
 	}
@@ -60,7 +60,7 @@ class Tests_XMLRPC_wp_getTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTerm( array( 1, 'editor', 'editor', 'category', 9999 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 		$this->assertEquals( __( 'Invalid term ID.' ), $result->message );
 	}
@@ -72,7 +72,7 @@ class Tests_XMLRPC_wp_getTerm extends WP_XMLRPC_UnitTestCase {
 
 		$result = $this->myxmlrpcserver->wp_getTerm( array( 1, 'editor', 'editor', 'category', self::$term_id ) );
 
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $result, $term );
 
 		// Check DataTypes
diff --git tests/phpunit/tests/xmlrpc/wp/getTerms.php tests/phpunit/tests/xmlrpc/wp/getTerms.php
index 1673975f1f..b67cbde140 100644
--- tests/phpunit/tests/xmlrpc/wp/getTerms.php
+++ tests/phpunit/tests/xmlrpc/wp/getTerms.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getTerms( array( 1, 'username', 'password', 'category' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -15,7 +15,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', '' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -24,7 +24,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', 'not_existing' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -33,7 +33,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getTerms( array( 1, 'subscriber', 'subscriber', 'category' ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 		$this->assertEquals( __( 'Sorry, you are not allowed to assign terms in this taxonomy.' ), $result->message );
 	}
@@ -45,7 +45,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 		$cat = wp_insert_term( 'term_' . __FUNCTION__ , 'category' );
 
 		$results = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', 'category' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		foreach( $results as $term ) {
 			$this->assertInternalType( 'int', $term['count'] );
@@ -71,7 +71,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 
 		// test fetching all terms
 		$results = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', $tax_name ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		$this->assertEquals( $num_terms, count( $results ) );
 		foreach ( $results as $term ) {
@@ -81,20 +81,20 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 		// test paged results
 		$filter = array( 'number' => 5 );
 		$results2 = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', $tax_name, $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$this->assertEquals( 5, count( $results2 ) );
 		$this->assertEquals( $results[1]['term_id'], $results2[1]['term_id'] ); // check one of the terms
 
 		$filter['offset'] = 10;
 		$results3 = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', $tax_name, $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results3 );
+		$this->assertNotIXRError( $results3 );
 		$this->assertEquals( $num_terms - 10, count( $results3 ) );
 		$this->assertEquals( $results[11]['term_id'], $results3[1]['term_id'] );
 
 		// test hide_empty (since none have been attached to posts yet, all should be hidden
 		$filter = array( 'hide_empty' => true );
 		$results4 = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', $tax_name, $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results4 );
+		$this->assertNotIXRError( $results4 );
 		$this->assertEquals( 0, count( $results4 ) );
 
 		unset($GLOBALS['wp_taxonomies'][$tax_name]);
@@ -111,7 +111,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 
 		$filter = array( 'orderby' => 'count', 'order' => 'DESC' );
 		$results = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', 'category', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$this->assertNotEquals( 0, count( $results ) );
 
 		foreach( $results as $term ) {
@@ -133,7 +133,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 		// search by full name
 		$filter = array( 'search' => $name );
 		$results = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', 'category', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$this->assertEquals( 1, count( $results ) );
 		$this->assertEquals( $name, $results[0]['name'] );
 		$this->assertEquals( $name_id, $results[0]['term_id'] );
@@ -141,7 +141,7 @@ class Tests_XMLRPC_wp_getTerms extends WP_XMLRPC_UnitTestCase {
 		// search by partial name
 		$filter = array( 'search' => substr( $name, 0, 10 ) );
 		$results2 = $this->myxmlrpcserver->wp_getTerms( array( 1, 'editor', 'editor', 'category', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results2 );
+		$this->assertNotIXRError( $results2 );
 		$this->assertEquals( 1, count( $results2 ) );
 		$this->assertEquals( $name, $results2[0]['name'] );
 		$this->assertEquals( $name_id, $results2[0]['term_id'] );
diff --git tests/phpunit/tests/xmlrpc/wp/getUser.php tests/phpunit/tests/xmlrpc/wp/getUser.php
index acef3c6a06..beda930f42 100644
--- tests/phpunit/tests/xmlrpc/wp/getUser.php
+++ tests/phpunit/tests/xmlrpc/wp/getUser.php
@@ -25,13 +25,13 @@ class Tests_XMLRPC_wp_getUser extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'username', 'password', 1 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
 	function test_invalid_user() {
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'administrator', 'administrator', 34902348908234 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 	}
 
@@ -40,7 +40,7 @@ class Tests_XMLRPC_wp_getUser extends WP_XMLRPC_UnitTestCase {
 		$editor_id = $this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'subscriber', 'subscriber', $editor_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -48,7 +48,7 @@ class Tests_XMLRPC_wp_getUser extends WP_XMLRPC_UnitTestCase {
 		$subscriber_id = $this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'subscriber', 'subscriber', $subscriber_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $subscriber_id, $result['user_id'] );
 	}
 
@@ -72,7 +72,7 @@ class Tests_XMLRPC_wp_getUser extends WP_XMLRPC_UnitTestCase {
 		$user_id = wp_insert_user( $user_data );
 
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'administrator', 'administrator', $user_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// check data types
 		$this->assertInternalType( 'string', $result['user_id'] );
@@ -111,7 +111,7 @@ class Tests_XMLRPC_wp_getUser extends WP_XMLRPC_UnitTestCase {
 		$editor_id = $this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'administrator', 'administrator', $editor_id, array() ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $editor_id, $result['user_id'] );
 
 		$expected_fields = array( 'user_id' );
@@ -122,7 +122,7 @@ class Tests_XMLRPC_wp_getUser extends WP_XMLRPC_UnitTestCase {
 		$editor_id = $this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'administrator', 'administrator', $editor_id, array( 'basic' ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $editor_id, $result['user_id'] );
 
 		$expected_fields = array( 'user_id', 'username', 'email', 'registered', 'display_name', 'nicename' );
@@ -138,7 +138,7 @@ class Tests_XMLRPC_wp_getUser extends WP_XMLRPC_UnitTestCase {
 		$fields = array( 'email', 'bio', 'user_contacts' );
 
 		$result = $this->myxmlrpcserver->wp_getUser( array( 1, 'administrator', 'administrator', $editor_id, $fields ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $editor_id, $result['user_id'] );
 
 		$expected_fields = array( 'user_id', 'email', 'bio' );
diff --git tests/phpunit/tests/xmlrpc/wp/getUsers.php tests/phpunit/tests/xmlrpc/wp/getUsers.php
index 1860fd11d3..62169e0c64 100644
--- tests/phpunit/tests/xmlrpc/wp/getUsers.php
+++ tests/phpunit/tests/xmlrpc/wp/getUsers.php
@@ -8,7 +8,7 @@ class Tests_XMLRPC_wp_getUsers extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$results = $this->myxmlrpcserver->wp_getUsers( array( 1, 'username', 'password' ) );
-		$this->assertInstanceOf( 'IXR_Error', $results );
+		$this->assertIXRError( $results );
 		$this->assertEquals( 403, $results->code );
 	}
 
@@ -16,7 +16,7 @@ class Tests_XMLRPC_wp_getUsers extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$results = $this->myxmlrpcserver->wp_getUsers( array( 1, 'subscriber', 'subscriber' ) );
-		$this->assertInstanceOf( 'IXR_Error', $results );
+		$this->assertIXRError( $results );
 		$this->assertEquals( 401, $results->code );
 	}
 
@@ -24,7 +24,7 @@ class Tests_XMLRPC_wp_getUsers extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'administrator' );
 
 		$result = $this->myxmlrpcserver->wp_getUsers( array( 1, 'administrator', 'administrator' ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// check data types
 		$this->assertInternalType( 'string', $result[0]['user_id'] );
@@ -49,7 +49,7 @@ class Tests_XMLRPC_wp_getUsers extends WP_XMLRPC_UnitTestCase {
 
 		$filter = array( 'role' => 'invalidrole' );
 		$results = $this->myxmlrpcserver->wp_getUsers( array( 1, 'administrator', 'administrator', $filter ) );
-		$this->assertInstanceOf( 'IXR_Error', $results );
+		$this->assertIXRError( $results );
 		$this->assertEquals( 403, $results->code );
 	}
 
@@ -63,14 +63,14 @@ class Tests_XMLRPC_wp_getUsers extends WP_XMLRPC_UnitTestCase {
 		// test a single role ('editor')
 		$filter = array( 'role' => 'editor' );
 		$results = $this->myxmlrpcserver->wp_getUsers( array( 1, 'administrator', 'administrator', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 		$this->assertCount( 1, $results );
 		$this->assertEquals( $editor_id, $results[0]['user_id'] );
 
 		// test 'authors', which should return all non-subscribers
 		$filter2 = array( 'who' => 'authors' );
 		$results2 = $this->myxmlrpcserver->wp_getUsers( array( 1, 'administrator', 'administrator', $filter2 ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results2 );
+		$this->assertNotIXRError( $results2 );
 		$this->assertCount( 3, array_intersect( array( $author_id, $editor_id, $administrator_id ), wp_list_pluck( $results2, 'user_id' ) ) );
 	}
 
@@ -104,7 +104,7 @@ class Tests_XMLRPC_wp_getUsers extends WP_XMLRPC_UnitTestCase {
 
 		$filter = array( 'orderby' => 'email', 'order' => 'ASC' );
 		$results = $this->myxmlrpcserver->wp_getUsers( array( 1, 'administrator', 'administrator', $filter ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $results );
+		$this->assertNotIXRError( $results );
 
 		$last_email = '';
 		foreach ( $results as $user ) {
diff --git tests/phpunit/tests/xmlrpc/wp/newComment.php tests/phpunit/tests/xmlrpc/wp/newComment.php
index 80e70ef32e..148c6acc23 100644
--- tests/phpunit/tests/xmlrpc/wp/newComment.php
+++ tests/phpunit/tests/xmlrpc/wp/newComment.php
@@ -13,7 +13,7 @@ class Tests_XMLRPC_wp_newComment extends WP_XMLRPC_UnitTestCase {
 			'content' => rand_str( 100 )
 		) ) );
  
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
  
 	function test_empty_comment() {
@@ -24,7 +24,7 @@ class Tests_XMLRPC_wp_newComment extends WP_XMLRPC_UnitTestCase {
 			'content' => ''
 		) ) );
  
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -40,7 +40,7 @@ class Tests_XMLRPC_wp_newComment extends WP_XMLRPC_UnitTestCase {
 			'content' => rand_str( 100 ),
 		) ) );
 
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -54,12 +54,12 @@ class Tests_XMLRPC_wp_newComment extends WP_XMLRPC_UnitTestCase {
 
 		// First time it's a valid comment
 		$result = $this->myxmlrpcserver->wp_newComment( $comment_args  );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// Run second time for duplication error
 		$result = $this->myxmlrpcserver->wp_newComment( $comment_args );
 
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
diff --git tests/phpunit/tests/xmlrpc/wp/newPost.php tests/phpunit/tests/xmlrpc/wp/newPost.php
index 3092aef637..1b718bc563 100644
--- tests/phpunit/tests/xmlrpc/wp/newPost.php
+++ tests/phpunit/tests/xmlrpc/wp/newPost.php
@@ -7,7 +7,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'username', 'password', array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -15,7 +15,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'subscriber', 'subscriber', array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -23,7 +23,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'author' );
 
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'author', 'author', array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 		$this->assertEquals( 'Content, title, and excerpt are empty.', $result->message );
 	}
@@ -33,7 +33,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 	}
 
@@ -42,7 +42,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'ID' => 103948 );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertNotEquals( '103948', $result );
 	}
 
@@ -51,7 +51,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_status' => 'publish' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_incapable_publish() {
@@ -59,7 +59,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_status' => 'publish' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'contributor', 'contributor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -68,7 +68,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_status' => 'private' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_incapable_private() {
@@ -76,7 +76,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_status' => 'private' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'contributor', 'contributor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -86,7 +86,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_author' => $other_author_id );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_incapable_other_author() {
@@ -95,7 +95,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_author' => $other_author_id );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'contributor', 'contributor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -104,7 +104,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_author' => 99999999 );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 404, $result->code );
 	}
 
@@ -113,7 +113,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 
 		$out = get_post( $result );
@@ -132,7 +132,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Post Thumbnail Test', 'post_thumbnail' => $attachment_id );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( $attachment_id, get_post_meta( $result, '_thumbnail_id', true ) );
 
 		remove_theme_support( 'post-thumbnails' );
@@ -143,7 +143,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_status' => 'foobar_status' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'author', 'author', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( 'draft', get_post_status( $result ) );
 	}
 
@@ -152,7 +152,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'sticky' => true );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'contributor', 'contributor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -161,7 +161,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'sticky' => true );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertTrue( is_sticky( $result ) );
 	}
 
@@ -170,7 +170,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_status' => 'private', 'sticky' => true );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -179,7 +179,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_format' => 'quote' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( 'quote', get_post_format( $result ) );
 	}
 
@@ -188,7 +188,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 
 		$post = array( 'post_title' => 'Test', 'post_format' => 'tumblr' );
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertEquals( '', get_post_format( $result ) );
 	}
 
@@ -202,7 +202,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 			)
 		);
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 
 		$post2 = array(
@@ -212,7 +212,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 			)
 		);
 		$result2 = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post2 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result2 );
+		$this->assertIXRError( $result2 );
 		$this->assertEquals( 401, $result2->code );
 	}
 
@@ -226,7 +226,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 			)
 		);
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -247,7 +247,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 			)
 		);
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		$post_tags = wp_get_object_terms( $result, 'post_tag', array( 'fields' => 'ids' ) );
 		$this->assertNotContains( $tag1['term_id'], $post_tags );
@@ -274,7 +274,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 			)
 		);
 		$result = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		// verify that cat2 was created
 		$cat2 = get_term_by( 'name', $cat2_name, 'category' );
 		$this->assertNotEmpty( $cat2 );
@@ -291,7 +291,7 @@ class Tests_XMLRPC_wp_newPost extends WP_XMLRPC_UnitTestCase {
 			)
 		);
 		$result2 = $this->myxmlrpcserver->wp_newPost( array( 1, 'editor', 'editor', $post2 ) );
-		$this->assertInstanceOf( 'IXR_Error', $result2 );
+		$this->assertIXRError( $result2 );
 		$this->assertEquals( 401, $result2->code );
 	}
 
diff --git tests/phpunit/tests/xmlrpc/wp/newTerm.php tests/phpunit/tests/xmlrpc/wp/newTerm.php
index 860e5c8dcb..f5f012f3eb 100644
--- tests/phpunit/tests/xmlrpc/wp/newTerm.php
+++ tests/phpunit/tests/xmlrpc/wp/newTerm.php
@@ -15,7 +15,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'username', 'password', array() ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -23,7 +23,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => '' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -32,7 +32,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => 'not_existing' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Invalid taxonomy.' ), $result->message );
 	}
@@ -41,7 +41,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'subscriber', 'subscriber', array( 'taxonomy' => 'category' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 		$this->assertEquals( __( 'Sorry, you are not allowed to create terms in this taxonomy.' ), $result->message );
 	}
@@ -50,7 +50,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => 'category', 'name' => '' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'The term name cannot be empty.' ), $result->message );
 	}
@@ -59,7 +59,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => 'post_tag', 'parent' => self::$parent_term_id, 'name' => 'test' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'This taxonomy is not hierarchical.' ), $result->message );
 	}
@@ -68,7 +68,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => 'category', 'parent' => 'dasda', 'name' => 'test' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 500, $result->code );
 	}
 
@@ -76,7 +76,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => 'category', 'parent' => 9999, 'name' => 'test' ) ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 		$this->assertEquals( __( 'Parent term does not exist.' ), $result->message );
 	}
@@ -86,7 +86,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => 'category', 'name' => 'test' ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 	}
 
@@ -94,7 +94,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result  = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', array( 'taxonomy' => 'category', 'parent' => self::$parent_term_id, 'name' => 'test' ) ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 	}
 
@@ -103,7 +103,7 @@ class Tests_XMLRPC_wp_newTerm extends WP_XMLRPC_UnitTestCase {
 
 		$taxonomy = array( 'taxonomy' => 'category', 'parent' => self::$parent_term_id, 'name' => 'test_all', 'description' => 'Test all', 'slug' => 'test_all' );
 		$result  = $this->myxmlrpcserver->wp_newTerm( array( 1, 'editor', 'editor', $taxonomy ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 		$this->assertStringMatchesFormat( '%d', $result );
 	}
 }
diff --git tests/phpunit/tests/xmlrpc/wp/restoreRevision.php tests/phpunit/tests/xmlrpc/wp/restoreRevision.php
index 75f5d74fa0..be9d1916af 100644
--- tests/phpunit/tests/xmlrpc/wp/restoreRevision.php
+++ tests/phpunit/tests/xmlrpc/wp/restoreRevision.php
@@ -23,7 +23,7 @@ class Tests_XMLRPC_wp_restoreRevision extends WP_XMLRPC_UnitTestCase {
 
 	function test_invalid_username_password() {
 		$result = $this->myxmlrpcserver->wp_restoreRevision( array( 1, 'username', 'password', $this->revision_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 403, $result->code );
 	}
 
@@ -31,7 +31,7 @@ class Tests_XMLRPC_wp_restoreRevision extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'subscriber' );
 
 		$result = $this->myxmlrpcserver->wp_restoreRevision( array( 1, 'subscriber', 'subscriber', $this->revision_id ) );
-		$this->assertInstanceOf( 'IXR_Error', $result );
+		$this->assertIXRError( $result );
 		$this->assertEquals( 401, $result->code );
 	}
 
@@ -39,7 +39,7 @@ class Tests_XMLRPC_wp_restoreRevision extends WP_XMLRPC_UnitTestCase {
 		$this->make_user_by_role( 'editor' );
 
 		$result = $this->myxmlrpcserver->wp_restoreRevision( array( 1, 'editor', 'editor', $this->revision_id ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 	}
 
 	function test_revision_restored() {
diff --git tests/phpunit/tests/xmlrpc/wp/uploadFile.php tests/phpunit/tests/xmlrpc/wp/uploadFile.php
index 8baa3f6cff..e15f85d420 100644
--- tests/phpunit/tests/xmlrpc/wp/uploadFile.php
+++ tests/phpunit/tests/xmlrpc/wp/uploadFile.php
@@ -25,7 +25,7 @@ class Tests_XMLRPC_wp_uploadFile extends WP_XMLRPC_UnitTestCase {
 
 
 		$result = $this->myxmlrpcserver->mw_newMediaObject( array( 0, 'editor', 'editor', $data ) );
-		$this->assertNotInstanceOf( 'IXR_Error', $result );
+		$this->assertNotIXRError( $result );
 
 		// check data types
 		$this->assertInternalType( 'string', $result['id'] );
