PHPUNIT - Testing a callback that is a new instance of class - php

Question

I have a class that calls a WordPress global function 'add_menu_page' This function receives a number of arguments, one of which is a callback that in this case creates a new instance of a class 'CreateAdminMountPoint'.
In my PHPUnit test I have mocked the admin_menu_page function and its expected 'with' arguments.
My problem lies with the callback class, in my test I have set the assertion to:
array(new CreateAdminMountPoint(array('slug' => 'brands')), 'addMountPoint')
This is obviously bad practice as my test now relies on a separate class rather than testing in isolation.
How can I change my test so it does not depend on CreateAdminMountPoint?
The Class
class CreateAdminMenus {
public function addMenuPages($tables) {
foreach( $tables as $menu ) {
add_menu_page(
$menu['title'],
$menu['title'],
$menu['wp-menu']['capability'],
'pup/' . $menu['title'] . '/edit.php',
[new CreateAdminMountPoint($menu), 'addMountPoint'], // Trying to test this without being dependant on CreatAdminMountPoint
$menu['wp-menu']['icon']
);
}
}
}
Test Case
class CreateAdminMenusTest extends LSMTestCase {
protected function setup() {
$this->tables = array(
'brands' =>
array(
'title' => 'title',
'slug' => 'brands',
'wp-menu' =>
array(
'capability' => 'capability',
'icon' => 'icon',
),
),
);
}
public function testMenusAreCreated() {
$adminMenus = new CreateAdminMenus;
$mock = $this->mockGlobalFunction('add_menu_page');
$mock->expects($this->exactly(1))
->method('add_menu_page')
->with(
'title',
'title',
'capability',
'pup/title/edit.php',
array(new CreateAdminMountPoint(array('slug' => 'brands')), 'addMountPoint'),
'icon'
);
$adminMenus->addMenuPages($this->tables);
}
}

Answer 1

The way your code is written now it's impossible to test it in any other way then you do now. Which actually isn't as bad as you might think. If I would see a test like this in a pull request I would approve it.
That being said, I can imagine that you do want to test it more thoroughly. Your best solution would be to use a CreateAdminMountPointBuilder class. So instead of creating the new object inline. You use your new class to build it. This way you can mock that class in your test and assert that the mocked response from the builder is put into your function call.
You can now also reuse the builder if you want to use it anywhere else in your project.
Hope it makes sense, otherwise I could add some sample code. Let me know!