Implement `assertNotWPError` in test suite

[danielbachhuber]

WP_Error often returns useful information about why a function is failed.

However, an assertion like $this->assertNotInstanceOf( 'WP_Error', $file ); isn't helpful to the test runner because it doesn't communicate the information conveyed by the WP_Error object.

Currently, someone running the test has to add some var_dump() debug (or similar) to read the contents of the returned error object.

It would be helpful to have an assertNotWPError assertion that communicated the contents of the WP_Error object when it actually is one.

Inspired by #42064

[johnbillion]

It's already there but there are a bunch of places in core that don't use it.

[danielbachhuber]

@johnbillion Should've grepped. Can we clean those up?

[johnbillion]

Yep definitely.

[birgire]

42065.diff​ changes:

$this->assertNotInstanceOf( 'WP_Error', ... )

to

$this->assertNotWPError( ... )

in the test files:

• tests/phpunit/tests/post/formats.php
• tests/phpunit/tests/customize/manager.php
• tests/phpunit/tests/customize/nav-menu-setting.php
• tests/phpunit/tests/image/editorImagick.php
• tests/phpunit/tests/image/editorGd.php
• tests/phpunit/tests/image/functions.php
• tests/phpunit/tests/admin/includesPost.php
• tests/phpunit/tests/ajax/CustomizeManager.php
• tests/phpunit/includes/testcase-rest-post-type-controller.php

This is the method's definition:

function assertNotWPError( $actual, $message = '' ) {
	if ( is_wp_error( $actual ) && '' === $message ) {
		$message = $actual->get_error_message();
	}
	$this->assertNotInstanceOf( 'WP_Error', $actual, $message );
}

where we see how the WP_Error error message is passed on to the $message argument of the assertNotInstandeOf method.

[johnbillion]

In 42863:

Build/Test Tools: Implement assertNotWPError() in appropriate places in the test suite.

Props birgire

Fixes #42065