Index: tests/phpunit/tests/functions/wpGetMimeTypes.php
===================================================================
--- tests/phpunit/tests/functions/wpGetMimeTypes.php	(nonexistent)
+++ tests/phpunit/tests/functions/wpGetMimeTypes.php	(working copy)
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * Test wp_get_mime_types().
+ *
+ * @group functions.php
+ */
+class Tests_wp_get_mime_types extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 47701
+	 */
+	public function test_all_mime_match() {
+		$mime_types_start = wp_get_mime_types();
+
+		$this->assertInternalType( 'array', $mime_types_start );
+		$this->assertNotEmpty( $mime_types_start );
+
+		add_filter( 'mime_types', '__return_empty_array' );
+		$mime_types_empty = wp_get_mime_types();
+		$this->assertSame( array(), $mime_types_empty );
+
+		remove_filter( 'mime_types', '__return_empty_array' );
+		$mime_types = wp_get_mime_types();
+		$this->assertInternalType( 'array', $mime_types );
+		$this->assertNotEmpty( $mime_types );
+		// and did it revert to the org after filter remove
+		$this->assertSame( $mime_types_start, $mime_types );
+	}
+}