'The massage does not contain stderr'

def test_container_without_stderr(self):

    client = make_fake_client()
    container = client.containers.get(FAKE_CONTAINER_ID)
    command = 'echo    Hello    World'
    exit_status = 42
    image = FAKE_IMAGE_ID
    stderr = None
    err = ContainerError(container, exit_status, command, image, stderr)
    msg = "Command    '{}'    in    image    '{}'    returned    non-zero    exit    status    {}".format(command, image, exit_status, stderr)
    assert (str(err) == msg)
