Unit testing Symfony 3.3项目中的测试表格（表格类型）

在Symfony 3.3项目中，我尝试测试以下简单表单：

class FooFormType extends AbstractType
{
    private $fooService;

    public function __construct(FooService $fooService)
    {
        $this->fooService = $fooService;
    }

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add(
                'bar',
                EntityType::class,
                [
                    'class' => Bar::class,
                    'choice_label' => 'title',
                    'placeholder' => 'Please select a bar',
                ]
            )
            ->add(
                'baz',
                ChoiceType::class,
                [
                    'choices' => $this->fooService->lorem(),
                ]
            )
        ;
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(
            [
                'data_class' => Foo::class,
            ]
        );
    }
}

我按照在上找到的说明编写了此（简化）测试：

不幸的是，引发了此异常：

Symfony\Component\Form\Exception\RuntimeException:Class“AppBundle\Entity\Bar”似乎不是托管条令实体。你忘了画地图了吗

这里有什么问题

class FooFormTypeTest extends TypeTestCase
{
    protected function getExtensions()
    {
        $fooServiceDummy = $this->createMock(FooService::class);
        $fooFormType = new FooFormType($fooServiceDummy);

        $managerRegistryDummy = $this->createMock(ManagerRegistry::class);
        $entityFormType = new EntityType($managerRegistryDummy);

        return [
            new PreloadedExtension([$fooFormType, $entityFormType], []),
        ];
    }

    /**
     * @test
     */
    public function submitValidData()
    {
        $form = $this->factory->create(FooFormType::class);
    }
}