public async Task OnGetAsync_GivenResponseReturnsNullWhenFetchingAllocationLines_ReturnsInternalServerError() { //Arrange Specification specification = CreateSpecification(); ApiResponse <Specification> apiResponse = new ApiResponse <Specification>(HttpStatusCode.OK, specification); ISpecsApiClient specsClient = CreateSpecsApiClient(); specsClient .GetSpecification(Arg.Is(specificationId)) .Returns(apiResponse); specsClient .GetFundingStreamByFundingStreamId(Arg.Is(fundingStreamId)) .Returns((ApiResponse <FundingStream>)null); CreateCalculationPageModel pageModel = CreatePageModel(specsClient); //Act IActionResult result = await pageModel.OnGetAsync(specificationId); //Assert result .Should() .BeAssignableTo <InternalServerErrorResult>(); }