How to test a class method that calls the void method of a property of that class and changes the state of that class?

Question

PHP

There are classes:

class Aaa {
    private $bbb;
    public $some_property = 10;

    function __construct(B $bbb){
        $this->bbb = $bbb;
    }

    public function some_func(){
        // ...
        $bbb->change_aaa_property($this);
        // ...
    }
}

class Bbb {
    function change_aaa_property(A $aaa){
        $aaa->some_property += 10;
    }
}

In the some_func() method of the Aaa class, the change_aaa_property() method is called on the $bbb object, which is a property of the Aaa class. In this change_aaa_property() property $some_property of class Aaa is changed.
I know that dependencies need to be replaced with mock objects, i.e. $bbb needs to be replaced with a mock object. But then how would the dummy $bbb object's change_aaa_property() method be able to change the $some_property of the $aaa object??? After all, mock objects, it seems, do not have an implementation of methods. And after testing some_func() , the value of $some_property remains the same (10).
In short, I want to understand how, when testing some_func() , to have the change_aaa_property() method of the dummy $bbb object change the $some_property property of the Aaa class.
Or perhaps there is another way to test some_func()?
I searched for a long time but did not find anything intelligible, maybe I was looking wrong. Yes, perhaps this is bad design and you shouldn’t do it, but is it really possible to do it?

Answer 1

$bbb = new Bbb();
$aaa = new Aaa($bbb);
$aaa->some_func();
$this->assertEquals(20, $aaa->some_property);