public async Task GetAlbumPhotosAsync_AlbumDoesNotExist_NotFound()
        {
            _albumServiceMock.Setup(x => x.GetAlbumPhotosAsync(200))
            .ReturnsAsync(null as IEnumerable <Photo>);

            var actionResult = await _albumController.GetAlbumPhotosAsync(200);

            var notFoundResult = actionResult as NotFoundResult;

            Assert.IsNotNull(notFoundResult);
            Assert.AreEqual(StatusCodes.Status404NotFound, notFoundResult.StatusCode);
        }