Symfony单元测试表单，使用jquery datepicker表单

I have a Roster entity in my Symfony project which contains two datetime fields.

Input field on FormType uses two single_text boxes, one for date one for time.

 $builder->add('serviceUserId', EntityType::class, array('class' => 'AppBundle:ServiceUser',
            'data' => $options['serviceUser']))
            ->add('rosterStartTime', DateTimeType::class,
                array('date_widget' => "single_text",
                    'time_widget' => "single_text",
                ))
            ->add('rosterEndTime', DateTimeType::class, array('date_widget' => "single_text",
                'time_widget' => "single_text",
            )

Can anyone tell me how to format the date I'm passing to this field in my Unit Test.

The nearest I've gotten is

      $client = static::createClient(array(), array(
        'PHP_AUTH_USER' => 'username',
        'PHP_AUTH_PW' => 'password',
    ));

    $date = new \DateTime('2015-04-01 08:00');

    //browse to an exsting service user and add a roster to that record
    $crawler = $client->request('GET', '/serviceuser/2');
    $crawler = $client->click($crawler->selectLink('Add New Roster')->link());

    // Fill in the form and submit it
    $form = $crawler->selectButton('Create')->form(array(
        'appbundle_roster[serviceUserId]' => 2,
        'appbundle_roster[rosterStartTime]'  => $date->format('yyyy-MM-dd'),

        'appbundle_roster[rosterStatus ]' => 1,
        'appbundle_roster[numberResourcesNeeded]' => 2,
        'appbundle_roster[customerId]' => 2,
    ));

It's failing with this error

     AppBundle\Tests\Controller\RosterControllerTest::testCompleteScenario
     InvalidArgumentException: Cannot set value on a compound field "appbundle_roster[rosterStartTime]".