public function testCollectionDiffsWithGivenCollection()
{
$e1 = new Entity();
$e1->id = 1;
$e2 = new Entity();
$e2->id = 2;
$e3 = new Entity();
$e3->id = 3;
$c1 = new Collection([$e1, $e2]);
$c2 = new Collection([$e2, $e3]);
$this->assertEquals(new Collection(array($e1)), $c1->diff($c2));
}
