PHPUnit: Testing Closure passed to Collaborator

Yes! Closure is callable, so you can just call __invoke() to the closure returned when test it! This is happen when we, for example, have a class and function that have closure inside it like the following:

class Awesome
{
    public function call($foo)
    {
        return function() use ($foo) {
            return $foo;
        };
    }
}

This can be tested with:

use Awesome;
use PHPUnit_Framework_TestCase;

class AwesomeTest extends PHPUnit_Framework_TestCase
{
    protected function setUp()
    {
        $this->awesome = new Awesome();
    }

    public function testCall()
    {
        $foo = 'foo';
        $call = $this->awesome->call($foo);
        $this->assertTrue(is_callable($call));

        $invoked = $call->__invoke();
        $this->assertEquals($foo, $invoked);
    }
}

We need an __invoke() call, as the closure never executed before it invoked. So, we need to call that.

On Collaborator Case

The problem is when we have a collaborator, and closure is processed inside the collaborator:

class Awesome
{
    private $awesomeDependency;

    public function __construct(AwesomeDependency $awesomeDependency)
    {
        $this->awesomeDependency = $awesomeDependency;
    }

    public function call($foo)
    {
        $closure = function() use ($foo) {
            return $foo;
        };
        return $this->awesomeDependency->call($closure);
    }
}

and the closure inside call only executed in the AwesomeDependency class:

class AwesomeDependency
{
    public function call($call)
    {
        return $call();
    }
}

Our test can be like the following:

use Awesome;
use AwesomeDependency;
use PHPUnit_Framework_TestCase;

class AwesomeTest extends PHPUnit_Framework_TestCase
{
    protected function setUp()
    {
        $this->awesomeDependency = $this->prophesize(AwesomeDependency::class);
        $this->awesome     = new Awesome($this->awesomeDependency->reveal());
    }

    public function testCall()
    {
        $foo = 'foo';
        $closure = function() use ($foo) {
            return $foo;
        };

        $this->awesomeDependency
             ->call($closure)
             ->will(function() use ($closure) {
                return $closure->__invoke();
             })
             ->shouldBeCalled();

        $call = $this->awesome->call($foo);
    }
}

As we can see, the $this->awesomeDependency is act as a mock, and calling __invoke() in will() is represent a $closure that already passed to the mock, not the original $closure one, and we will get partial coverage:

We know now, it won’t coverable as completed! What we can do? A refactor! But wait, it may be a legacy code, an aggressive refactor may cause problem, so a little but works patch may work for it.

• Make a $closure as class property, and add mutator and accessor for it.

class Awesome
{
    private $closure;

    // ...

    public function setClosure($closure)
    {
        $this->closure = $closure;
    }

    public function getClosure()
    {
        return $this->closure;
    }

    // ...
}

• Set $closure property when call call() function:

class Awesome
{
    // ...
    public function call($foo)
    {
        $this->setClosure(function() use ($foo) {
            return $foo;
        });

        return $this->awesomeDependency->call($this->getClosure());
    }
}

• And in tests, we can now has:

class AwesomeTest extends PHPUnit_Framework_TestCase
{
    // ...
    public function testCall()
    {
        $foo = 'foo';
        $closure = function() use ($foo) {
            return $foo;
        };
        $awesome = $this->awesome;

        $this->awesomeDependency
             ->call($closure)
             ->will(function() use ($awesome) {
                return $awesome->getClosure()->__invoke();
            })
            ->shouldBeCalled();

        $call = $this->awesome->call($foo);
        $this->assertEquals($foo, $call);
    }
}

Need a better way? We can replace a closure with an array callback, so, we add additional function that called via call_user_func_array():

class Awesome
{
    public function call($foo)
    {
        return $this->awesomeDependency->call(call_user_func_array(
            [$this, 'onFoo'],
            [$foo]
        ));
    }

    public function onFoo($foo)
    {
        return function() use ($foo) {
            return $foo;
        };
    }
}

And in our tests, we can do:

    public function testCall()
    {
        $foo = 'foo';
        $closure = function() use ($foo) {
            return $foo;
        };
        $awesome = $this->awesome;
        $this->awesomeDependency->call($closure)
             ->will(function() use ($awesome, $foo) {
                 return $awesome->onFoo($foo)->__invoke();
             })
            ->shouldBeCalled();

        $call = $this->awesome->call($foo);
        $this->assertEquals($foo, $call);
    }

And, we now have a fully coverage too: