public async Task GetCalculationByCalculationSpecificationId_GivenACalculationIsNotFound_ShouldReturnNotFoundObjectResult()
{
//Arrange
const string calcSpecId = "CalcSpecId";
ICalculationsRepository mockCalculationRepository = Substitute.For <ICalculationsRepository>();
mockCalculationRepository
.GetCalculationByCalculationSpecificationId(calcSpecId)
.Returns(Task.FromResult((Calculation)null));
CalculationService service = CreateCalculationService(calculationsRepository: mockCalculationRepository);
//Act
IActionResult result = await service.GetCalculationByCalculationSpecificationId(calcSpecId);
//Assert
result
.Should()
.BeOfType <NotFoundObjectResult>();
}