public void TestDeleteByDish()
        {
            // Arrange
            var dish1 = new Dish(
                "Eis",
                "Ice cream",
                2.0M,
                Category.Dessert,
                TimeOfDay.Weekdays,
                true,
                2
                );

            // Act
            var dish2 = crudService.Create(dish1);

            Assert.NotNull(dish2);
            crudService.DeleteByDish(dish2);

            // Assert
            var dish3 = crudService.ReadById(dish2.Id);

            Assert.Null(dish3);
        }