Tests: Use error assertions in Customizer nav menu tests.

Use `assertWPError()` in the Customizer navigation menu tests. Preserve the existing error-code and successful-result assertions.

Developed in: #14570

Props shailu25.
See #65819.


git-svn-id: https://develop.svn.wordpress.org/trunk@64653 602fd350-edb4-49c9-b593-d223f7449a82

Author: lancewillett

tests/phpunit/tests/customize/nav-menus.php

@@ -128,12 +128,12 @@ public function test_load_available_items_query_returns_wp_error() {
 
 		// Invalid post type $obj_name.
 		$items = $menus->load_available_items_query( 'post_type', 'invalid' );
-		$this->assertInstanceOf( 'WP_Error', $items );
+		$this->assertWPError( $items );
 		$this->assertSame( 'nav_menus_invalid_post_type', $items->get_error_code() );
 
 		// Invalid taxonomy $obj_name.
 		$items = $menus->load_available_items_query( 'taxonomy', 'invalid' );
-		$this->assertInstanceOf( 'WP_Error', $items );
+		$this->assertWPError( $items );
 		$this->assertSame( 'invalid_taxonomy', $items->get_error_code() );
 	}
 
@@ -686,7 +686,7 @@ public function test_insert_auto_draft_post() {
 		$menus = new WP_Customize_Nav_Menus( $this->wp_customize );
 
 		$r = $menus->insert_auto_draft_post( array() );
-		$this->assertInstanceOf( 'WP_Error', $r );
+		$this->assertWPError( $r );
 		$this->assertSame( 'unknown_post_type', $r->get_error_code() );
 
 		// Non-existent post types allowed as of #39610.
@@ -700,7 +700,7 @@ public function test_insert_auto_draft_post() {
 		$this->assertSame( $this->wp_customize->changeset_uuid(), get_post_meta( $r->ID, '_customize_changeset_uuid', true ) );
 
 		$r = $menus->insert_auto_draft_post( array( 'post_type' => 'post' ) );
-		$this->assertInstanceOf( 'WP_Error', $r );
+		$this->assertWPError( $r );
 		$this->assertSame( 'empty_title', $r->get_error_code() );
 
 		$r = $menus->insert_auto_draft_post(
@@ -710,7 +710,7 @@ public function test_insert_auto_draft_post() {
 				'post_type'   => 'post',
 			)
 		);
-		$this->assertInstanceOf( 'WP_Error', $r );
+		$this->assertWPError( $r );
 		$this->assertSame( 'status_forbidden', $r->get_error_code() );
 
 		$r = $menus->insert_auto_draft_post(