Unit test for mocking a method called by new class object

Question

I am writing unit test for an existing code which is like this

class someClass {
    public function __construct() { ... }

    public function someFoo($var) {
        ...
        $var = "something";
        ...
        $model = new someClass();
        model->someOtherFoo($var);
    }

    public someOtherFoo($var){
         // some code which has to be mocked
    }
}

Here how should I be able to mock the call to function "someOtherFoo" such that it doesn't execute "some code" inside someOtherFoo?

class someClassTest {
   public function someFoo() {
      $fixture = $this->getMock('someClass ', array('someOtherFoo'));
      $var = "something";
      ....
      // How to mock the call to someOtherFoo() here
   }

}

Is it possible to mock out the constructor so that it returns my own constructed function or variable?

Thanks

Answer 1

Wherever you have new XXX(...) in a method under test, you are doomed. Extract the instantiation to a new method--createSomeClass(...)--of the same class. This allows you to create a partial mock of the class under test that returns a stubbed or mock value from the new method.

class someClass {
    public function someFoo($var) {
        $model = $this->createSomeClass();  // call method instead of using new
        model->someOtherFoo($var);
    }

    public function createSomeClass() {  // now you can mock this method in the test
        return new someClass();
    }

    public function someOtherFoo($var){
         // some code which has to be mocked
    }
}

In the test, mock createSomeClass() in the instance on which you call someFoo(), and mock someOtherFoo() in the instance that you return from the first mocked call.

function testSomeFoo() {
    // mock someOtherFoo() to ensure it gets the correct value for $arg
    $created = $this->getMock('someClass', array('someOtherFoo'));
    $created->expects($this->once())
            ->method('someOtherFoo')
            ->with('foo');

    // mock createSomeClass() to return the mock above
    $creator = $this->getMock('someClass', array('createSomeClass'));
    $creator->expects($this->once())
            ->method('createSomeClass')
            ->will($this->returnValue($created));

    // call someFoo() with the correct $arg
    $creator->someFoo('foo');
}

Keep in mind that because the instance is creating another instance of the same class, two instances will normally be involved. You could use the same mock instance here if it makes it clearer.

function testSomeFoo() {
    $fixture = $this->getMock('someClass', array('createSomeClass', 'someOtherFoo'));

    // mock createSomeClass() to return the mock
    $fixture->expects($this->once())
            ->method('createSomeClass')
            ->will($this->returnValue($fixture));

    // mock someOtherFoo() to ensure it gets the correct value for $arg
    $fixture->expects($this->once())
            ->method('someOtherFoo')
            ->with('foo');

    // call someFoo() with the correct $arg
    $fixture->someFoo('foo');
}