How to mock an Object Factory - php

Question

I use Factories (see http://www.php.net/manual/en/language.oop5.patterns.php for the pattern) a lot to increase the testability of our code. A simple factory could look like this:
class Factory
{
public function getInstanceFor($type)
{
switch ($type) {
case 'foo':
return new Foo();
case 'bar':
return new Bar();
}
}
}
Here is a sample class using that factory:
class Sample
{
protected $_factory;
public function __construct(Factory $factory)
{
$this->_factory = $factory;
}
public function doSomething()
{
$foo = $this->_factory->getInstanceFor('foo');
$bar = $this->_factory->getInstanceFor('bar');
/* more stuff done here */
/* ... */
}
}
Now for proper unit testing I need to mock the object that will return stubs for the classes, and that is where I got stuck. I thought it would be possible to do it like this:
class SampleTest extends PHPUnit_Framework_TestCase
{
public function testAClassUsingObjectFactory()
{
$fooStub = $this->getMock('Foo');
$barStub = $this->getMock('Bar');
$factoryMock = $this->getMock('Factory');
$factoryMock->expects($this->any())
->method('getInstanceFor')
->with('foo')
->will($this->returnValue($fooStub));
$factoryMock->expects($this->any())
->method('getInstanceFor')
->with('bar')
->will($this->returnValue($barStub));
}
}
But when I run the test, this is what I get:
F
Time: 0 seconds, Memory: 5.25Mb
There was 1 failure:
1) SampleTest::testDoSomething
Failed asserting that two strings are equal.
--- Expected
+++ Actual
## ##
-bar
+foo
FAILURES!
Tests: 1, Assertions: 0, Failures: 1.
So obviously it is not possible to let a mock object return different values depending on the passed method arguments this way.
How can this be done?

Answer 1

The problem is that the PHPUnit Mocking doesn't allow you to do this:
$factoryMock->expects($this->any())
->method('getInstanceFor')
->with('foo')
->will($this->returnValue($fooStub));
$factoryMock->expects($this->any())
->method('getInstanceFor')
->with('bar')
->will($this->returnValue($barStub));
You can only have one expects per ->method();. It is not aware of the fact that the parameters to ->with() differ!
So you just overwrite the first ->expects() with the second one. It's how those assertions are implemented and it's not what one would expect. But there are workarounds.
You need to define one expects with both behaviors / return values!
See: Mock in PHPUnit - multiple configuration of the same method with different arguments
When adapting the example to your problem it could look like this:
$fooStub = $this->getMock('Foo');
$barStub = $this->getMock('Bar');
$factoryMock->expects($this->exactly(2))
->method('getInstanceFor')
->with($this->logicalOr(
$this->equalTo('foo'),
$this->equalTo('bar')
))
->will($this->returnCallback(
function($param) use ($fooStub, $barStub) {
if($param == 'foo') return $fooStub;
return $barStub;
}
));

Answer 2

Create a simple stub factory class whose constructor takes the instances it should return.
class StubFactory extends Factory
{
private $items;
public function __construct(array $items)
{
$this->items = $items;
}
public function getInstanceFor($type)
{
if (!isset($this->items[$type])) {
throw new InvalidArgumentException("Object for $type not found.");
}
return $this->items[$type];
}
}
You can reuse this class in any unit test.
class SampleTest extends PHPUnit_Framework_TestCase
{
public function testAClassUsingObjectFactory()
{
$fooStub = $this->getMock('Foo');
$barStub = $this->getMock('Bar');
$factory = new StubFactory(array(
'foo' => $fooStub,
'bar' => $barStub,
));
...no need to set expectations on $factory...
}
}
For completeness, if you don't mind writing brittle tests, you can use at($index) instead of any() in your original code. This will break if the system under test changes the order or number of calls to the factory, but it's easy to write.
$factoryMock->expects($this->at(0))
->method('getInstanceFor')
->with('foo')
->will($this->returnValue($fooStub));
$factoryMock->expects($this->at(1))
->method('getInstanceFor')
->with('bar')
->will($this->returnValue($barStub));

Answer 3

you should change your "business logic" ... i mean you don't have to pass Factory to the Sample constructor, you have to pass the exact parameters you need