public void TestAddFilm()
        {
            var mockSet     = new Mock <DbSet <Film> >();
            var mockContext = new Mock <DVDRentalContext>();

            mockContext.Setup(context => context.Films).Returns(mockSet.Object);
            repository = new FilmContext(mockContext.Object);

            repository.AddFilm(new Models.Film {
                Title = "Unit test paradise", Description = "Explaining art of unit testing", Length = 102
            });
            mockSet.Verify(m => m.Add(It.IsAny <DatabaseClient.TableEntity.Film>()), Times.Once());
            mockContext.Verify(m => m.SaveChanges(), Times.Once());
        }