public async Task PerformSearch_WhenFindCalculationsServiceReturnsNotFound_ThenNullReturned() { // Arrange ICalculationsApiClient calcsClient = Substitute.For <ICalculationsApiClient>(); ILogger logger = Substitute.For <ILogger>(); IMapper mapper = MappingHelper.CreateFrontEndMapper(); ICalculationSearchService calculationSearchService = new CalculationSearchService(calcsClient, mapper, logger); ApiResponse <SearchResults <CalculationSearchResult> > expectedServiceResult = null; calcsClient .FindCalculations(Arg.Any <SearchFilterRequest>()) .Returns(expectedServiceResult); SearchRequestViewModel request = new SearchRequestViewModel(); // Act CalculationSearchResultViewModel result = await calculationSearchService.PerformSearch(request); // Assert result.Should().BeNull(); }