Index: tests/phpunit/tests/user.php
--- tests/phpunit/tests/user.php Base (BASE)
+++ tests/phpunit/tests/user.php Locally Modified (Based On LOCAL)
@@ -699,4 +699,24 @@
 		$user = get_userdata( $user->ID );
 		$this->assertEmpty( $user->user_activation_key );
 	}
+	/**
+	 * @ticket 32158
+	 */
+	function test_email_case(){
+		// Create a test user with a lower-case email address.
+		$user_id = $this->factory->user->create( array(
+			'role' => 'author',
+			'user_login' => 'test_wp_update_user',
+			'user_pass' => 'password',
+			'user_email' => 'test@test.com',
+		) );
+		// Alter the case of the email address (which stays the same).
+		$userdata = array(
+			'ID'            => $user_id,
+			'user_email'    => 'test@TEST.com',
+		);
+		$update	= wp_update_user( $userdata );
+		
+		$this->assertFalse( is_wp_error( $update ) );
 }
+}