public function testDiff()
{
$diffCollection = $this->subclassCollection->diff($this->subclassCollection);
$this->assertTrue($diffCollection->isEmpty());
$diffCollection = $this->subclassCollection->diff($this->getMockSubclassCollection());
$this->assertEquals($this->subclassCollection->get(1), $diffCollection->get(1));
$this->assertEquals($this->subclassCollection->get(2), $diffCollection->get(2));
$subclassCollection = $this->getMockSubclassCollection();
$subclassCollection->add($this->subclassCollection->get(1));
$diffCollection = $this->subclassCollection->diff($subclassCollection);
$this->assertCount(1, $diffCollection);
$this->assertEquals($this->subclassCollection->get(2), $diffCollection->first());
}
