public void AddToQuantityShouldIncreaseTheQuantityWithOne() { DbContextOptions <UltimateMoviesDbContext> options = new DbContextOptionsBuilder <UltimateMoviesDbContext>() .UseInMemoryDatabase(databaseName: "Carts_AddToQuantity_Database") .Options; UltimateMoviesDbContext db = new UltimateMoviesDbContext(options); ICartsService cartsService = new CartsService(db); db.Users.Add(new UMUser { UserName = "******" }); db.SaveChanges(); db.CartMovies.Add(new CartMovie { MovieId = 1, UserId = db.Users.Last().Id, Quantity = 1 }); db.SaveChanges(); cartsService.AddToQuantity("Test", 1); int quantity = db.CartMovies.Last().Quantity; Assert.Equal(2, quantity); }