serializer = SerializerBuilder::create() ->addDefaultHandlers()//load PropelCollectionHandler ->build(); } public function testSerializePropelObjectCollection() { $collection = new \PropelObjectCollection(); $collection->setData(array(new TestSubject('lolo'), new TestSubject('pepe'))); $json = $this->serializer->serialize($collection, 'json'); $data = json_decode($json, true); $this->assertCount(2, $data); //will fail if PropelCollectionHandler not loaded foreach ($data as $testSubject) { $this->assertArrayHasKey('name', $testSubject); } } } class TestSubject { protected $name; public function __construct($name) { $this->name = $name; } }