PHPunit: How to change Mock object propriety from an external function - php

Question

I am using Symfony and I'm trying to test the addStudentCard function in "Student" class, which adds a "StudentCard" object to $studentCards array collection propriety AND a "Student" object to $student propriety in "StudentCard" class. This is how I did it:
class StudentCard {
private $student;
public function getStudent();
public function setStudent();
//...
}
class Student {
private $studentCards;
public function getStudentCards();
public function addStudentCard(StudentCard $studentCard){
$studentCard->setStudent($this);
$this->studentCards[] = $studentCard;
return $this;
//...
}
What I want to achieve is to test this addStudentCard function using a MockBuilder, I have already done this without using mocks by doing:
class StudentTest extends AbstractTestCase {
public function testAddStudentCard(){
$studentCard = new StudentCard();
$student = new Student();
$student->addStudentCard($studentCard);
$student->assertSame($studentCard, $student->getStudentCards()[0]);
$student->assertSame($student, $studentCard->getStudent());
}
This works as expected with no problem.
What I would like is to replace the line:
$studentCard = new StudentCard();
with something like this:
$studentCard = $this->getMockBuilder(StudentCard::class)->getMock();
But what I get is the error:
Failed asserting that null is identical to an object of class Student.

Answer 1

The problem with your scenario is, that you are asserting that the mock returns the original student:
$student->assertSame($student, $studentCard->getStudent());
If the $studentCard is a Mock object, it doesn't return the original object unless you tell it to do so. But since you are already using a mock, there is no need to test that.
What you actually want to test in this case is, that the $student was assigned back to the $studentCard. That is what expectations are for.
So in your particular case you would go with:
$studentCard->expects($this->once())->method('setStudent')->with($student);
// ...
$student->addStudentCard($studentCard);
Make sure that you have the line there (as I shown in the code) before you call addStudentCard, otherwise the test will fail that the expectation has not been met.
After you set the expectations, there is no need to run any assertions (and you should not) on the mock objects.

Answer 2

The answer Ondrej Führer provided is the right answer to the problem I described.
I had also a removeStudentCard method that deletes the student from the studentCard object, so $this->once() was not appropriate for my case. In order to test this, I did exactly the same thing Ondrej Führer suggested with some modifications, so the code line I added was:
$studentCard->expects($this->exactly(2))->method('setStudent')->withConsecutive(
[$student],
[null]
);
//...
$student->addStudentCard($studentCard);
//...
$student->removeStudentCard($studentCard);
This is self explaining, the method setContact is expected to be called exaclty two times with $student as an argument for the first time, and null in the second call.
Hopefully this would be helpful for anyone looking to do something similar.