public async Task GetByIdAsyncWhenInvalidIdReturnsDietNotFoundResponse()
{
// Arrange
var mockDietRepository = GetDefaultIDietRepositoryInstance();
var dietId = 1;
mockDietRepository.Setup(r => r.FindById(dietId))
.Returns(Task.FromResult <Diet>(null));
var mockUnitOfWork = GetDefaultIUnitOfWorkInstance();
var service = new DietService(mockDietRepository.Object, mockUnitOfWork.Object);
// Act
DietResponse result = await service.GetByIdAsync(dietId);
var message = result.Message;
// Assert
message.Should().Be("Diet not found");
}