Mocking class within class

Imagine a case where you need to create an instance of a class and use it within the same method:

// Point.php
<?php
namespace App;

class Point {
    public function setPoint($x, $y) {
        echo "Point (" . $x . ", " . $y . ")" . PHP_EOL;
    }
}

// Rectangle.php
<?php
namespace App;
use App\Point;

class Rectangle {
    public function create($x1, $y1, $x2, $y2) {
        $a = new Point();
        $a->setPoint($x1, $y1);

        $b = new Point();
        $b->setPoint($x2, $y1);

        $c = new Point();
        $c->setPoint($x2, $y2);

        $d = new Point();
        $d->setPoint($x1, $y2);

        $this->draw([$a, $b, $c, $d]);
    }

    public function draw($points) {
        echo "Do something with the points";
    }
}

And that you want to test that a logic in Rectangle->create() calls properly each used thing - in this case calls Point->setPoint(), but Rectangle->draw() does some graphical stuff that you want to avoid calling.

You set the mocks for App\Point and App\Rectangle:

<?php
class MyTest extends PHPUnit\Framework\TestCase {
    public function testCreate() {
        $point = Mockery::mock("App\Point");
        // check if our mock is called
        $point->shouldReceive("setPoint")->andThrow(Exception::class);

        $rect = Mockery::mock("App\Rectangle")->makePartial();
        $rect->shouldReceive("draw");

        $rect->create(0, 0, 100, 100);  // does not throw exception
        Mockery::close();
    }
}

and the test does not work. Why? The mocking relies on the class not being present yet, but the class is autoloaded therefore the mock alone for App\Point is useless which you can see with echo being executed.

Mocks however work for the first class in the order of loading i.e. App\Rectangle, which loads the App\Point class. In more complex example that would be a single point that initiates the whole loading (use Class) such as:

A        // main loading initiator
|- B     // another loading initiator
|  |-E
|  +-G
|
|- C     // another loading initiator
|  +-F
|
+- D

That basically means that the loading prevents mocking and for each such a loading initiator there needs to be implemented a workaround. Overloading is one approach, however it polutes the global state. In this case we try to completely avoid the global state polution with custom new Class() behavior per loading initiator and that can be mocked easily in few critical places.

That being said, although we can’t stop loading, we can return mocks. Let’s look at Rectangle->create() method:

class Rectangle {
    public function newPoint() {
        return new Point();
    }

    public function create($x1, $y1, $x2, $y2) {
        $a = $this->newPoint();
        $a->setPoint($x1, $y1);
        ...
    }
    ...
}

We create a custom function to encapsulate new keyword that would otherwise just use the autoloaded class App\Point and in our test we mock that function so that it returns our mock:

<?php
class MyTest extends PHPUnit\Framework\TestCase {
    public function testCreate() {
        $point = Mockery::mock("App\Point");
        // check if our mock is called
        $point->shouldReceive("setPoint")->andThrow(Exception::class);

        $rect = Mockery::mock("App\Rectangle")->makePartial();
        $rect->shouldReceive("draw");

        // pass the App\Point mock into App\Rectangle as an alternative
        // to using new App\Point() in-place.
        $rect->shouldReceive("newPoint")->andReturn($point);

        $this->expectException(Exception::class);
        $rect->create(0, 0, 100, 100);
        Mockery::close();
    }
}

If we run this test now, it should pass. For more complex cases we’d find the next loader in the program flow and proceed with wrapping and passing mock instances with predefined behavior into already existing classes.