How to mock 'find' method in Symfony 3

I´m trying to mock the find method of the EntityRepository,so that the test doesn't look for the data in the database but it doesn´t seem to work. Here's the setUp method of the test class

public function setUp()
{
    parent::setUp();

    $this->client = static::createClient();
    $this->peopleManager = $this->getMockBuilder(PeopleManager::class)
        ->setMethods(['createPerson','peopleUpdate', 'peopleDelete', 'peopleRead'])
        ->disableOriginalConstructor()
        ->getMock();

   $this->repository = $this->getMockBuilder(EntityRepository::class)
       ->disableOriginalConstructor()
       ->getMock();

   $this->em = $this->getMockBuilder(EntityManager::class)
       ->disableOriginalConstructor()
       ->getMock(); 
}

This is the method where we call the find function

public function updatePersonAction($id, Request $request)
{
    $repository = $this->getDoctrine()->getRepository('GeneralBundle:People');
    $person= $repository->find($id);
    if($person)
    {
        $data = $request->request->get('array');
        $createdPeople = array();
        $UpdatedPerson = "";
        foreach($data as $content)
        {
            $prueba = $this->get('people.manager');
            $UpdatedPerson = $prueba->peopleUpdate(
                $person,
                $content['name'],
                $content['surname'],
                $content['secondSurname'],
                $content['nationality'],
                $content['birthday'],
                $content['identityCard'],
                $content['identityCardType']
            );
            array_push($createdPeople, $person);
        }
        $serializedEntity = $this->get('serializer')->serialize($UpdatedPerson, 'json');
        return new Response($serializedEntity);
    } else {
        $serializedEntity = $this->get('serializer')->serialize('Doesn\'t exists any person with this id', 'json');
        return new Response($serializedEntity);
    }
}

The debugger shows that the peoplemanager class is mocked but it doesn't mock the entity manager and the repository.

Thank you <3.