How to mock a Doctrine Custom Repository using Profecy

DefaultRepository.php

<?php
declare(strict_types = 1);

namespace App;

use Doctrine\ORM\EntityRepository;
use App\Exception\EntityNotFoundException;

class DefaultRepository extends EntityRepository
{
    /**
     * Searches for an object. If not found, throws an exception.
     * This is only a shorthand for $repo->find($id) in order to avoid
     * "if" statements scattered throughout code.
     * 
     * @see http://ocramius.github.io/doctrine-best-practices/#/97
     * @param $id
     * @return object
     * @throws EntityNotFoundException
     */
    public function get($id)
    {
        $object = $this->_em->find($this->getEntityName(), $id);

        if ($object == null) {
            throw new EntityNotFoundException();
        }

        return $object;
    }
}

DefaultRepositoryTest.php

<?php
declare(strict_types = 1);

namespace App;

use PHPUnit_Framework_TestCase as TestCase;
use Doctrine\ORM\EntityManager;
use Doctrine\ORM\Mapping\ClassMetadata;
use Prophecy\Prophecy\ObjectProphecy;
use Doctrine\ORM\EntityRepository;

class DefaultRepositoryTest extends TestCase
{
    /**
     * @var EntityManager|ObjectProphecy
     */
    protected $entityManager;
    /**
     * @var ClassMetadata|ObjectProphecy
     */
    protected $classMetadata;

    public function setUp()
    {
        $this->entityManager = $this->prophesize(EntityManager::class);
        $this->classMetadata = $this->prophesize(ClassMetadata::class);
    }

    /**
     * @expectedException \App\Exception\EntityNotFoundException
     */
    public function testThrowsExceptionWhenItemWasNotFound()
    {
        $id = 999;
        $this->entityManager->find(DefaultRepositoryTestDumb::class, $id)->willReturn(null);
        $this->classMetadata->name = DefaultRepositoryTestDumb::class;

        $repository = new DefaultRepository($this->entityManager->reveal(), $this->classMetadata->reveal());
        $repository->get($id);
    }

    public function testGetReturnsTheObjectWhenItWasFound()
    {
        $id = 1;
        $found = new DefaultRepositoryTest();
        $this->entityManager->find(DefaultRepositoryTestDumb::class, $id)->willReturn($found);
        $this->classMetadata->name = DefaultRepositoryTestDumb::class;

        $repository = new DefaultRepository($this->entityManager->reveal(), $this->classMetadata->reveal());
        $this->assertEquals($found, $repository->get($id));
    }
}

class DefaultRepositoryTestDumb
{

}