public function testFindSlice()
 {
     $entities = array('one' => new TypeOne(), 'two' => new TypeTwo(), 'three' => new TypeOne());
     $expected = array('two' => $entities['two']);
     $registry = new Registry();
     $registry->merge($entities);
     $this->assertEquals($expected, $registry->find(null, -2, 1));
 }