Mocking LINQ-to-SQL navigation property for an object created at runtime w/ NSubstitute

Question

I am stumped here. I have struggled to find any viable answer to my question both here and within NSubstitute's documentation.

I'm trying to unit test a service method where, after an object is added to the repository, I access the navigation properties of that object to do other work. When the unit test gets to the point in the code where the new object's navigation properties are accessed, I get a NullReferenceException. I understand WHY I get the exception, because I haven't told it what it should return in the mocking, but what I cannot figure out is HOW to tell the unit test what to return when accessing the navigation properties. This, all because the object is created at run-time.

For brevity sake, I will only include the portions of the methods that are relevant.

// This is the method I am trying to unit test
public void SaveSelectedResultsMeasures(SelectResultsMeasuresViewModel model)
{
    // validate the model
    ...

    var cpf = this.repository.GetCareerPlanningFormByID(model.CareerPlanningFormID);

    model.ResultsMeasuresSections.ToList().ForEach(resultsMeasuresSection =>
    {
        var selectedResultsMeasuresSection = cpf.SelectedResultsMeasuresSections
                                                .Where(o => o.ResultsMeasuresSectionID == resultsMeasuresSection.SectionID)
                                                .ToMaybe();

        if (resultsMeasuresSection.IsSelected)
        {
            if (!selectedResultsMeasuresSection.HasValue)
            {
                // here is where the new object is being created and added to the repository
                cpf.SelectedResultsMeasuresSections.Add(new SelectedResultsMeasuresSection
                {
                    CareerPlanningFormID = cpf.CareerPlanningFormID,
                    IsDeleted = false,
                    ResultsMeasuresSectionID = resultsMeasuresSection.SectionID,
                    RepeatNumberOfOccurrences = resultsMeasuresSection.RepeatNumberOfOccurrences ?? 1
                });
                this.repository.Commit();

                // now that the add has been committed, i get the object i just created
                var newSelectedResultsMeasuresSection = cpf.SelectedResultsMeasuresSections
                    .Where(o => o.ResultsMeasuresSectionID == resultsMeasuresSection.SectionID)
                    .Single();

                // here is where i access the navigation properties of that object
                // this works just fine, just need to figure out how to unit test it so that i can continue to test the code inside the block
                // when the unit test hits this point, this is where I get the NullReferenceException
                newSelectedResultsMeasuresSection.ResultsMeasuresSection.ResultsMeasures.ToList().ForEach(rm =>
                {
                    // code here...
                }
            }
        }
    }
}

// This is the unit test
[TestClass]
[ExcludeFromCodeCoverage]
public class CareerPlanningFormServiceTest
{
    private readonly IPartnerPerformanceManagementConfiguration configuration;
    private readonly IPartnerPerformanceManagementRepository repository;
    private readonly IPrincipal currentUser;
    private readonly CareerPlanningFormService target;

    public CareerPlanningFormServiceTest()
    {
        this.configuration = Substitute.For<IPartnerPerformanceManagementConfiguration>();
        this.repository = Substitute.For<IPartnerPerformanceManagementRepository>();
        this.currentUser = Substitute.For<IPrincipal>();

        this.target = new CareerPlanningFormService(
            this.configuration,
            this.repository,
            this.currentUser);
    }

    /// <summary>
    /// Tests the SaveSelectedResultsMeasures method.
    /// Test success when adding a new SelectedResultsMeasuresSection
    /// </summary>
    [TestMethod]
    [TestCategory("CareerPlanningFormService")]
    [TestCategory("CareerPlanningFormService - SaveSelectedResultsMeasures")]
    public void SaveSelectedResultsMeasures_Test_Success_Add_SelectedResultsMeasuresSection()
    {
        // Arrange
        var model = new SelectResultsMeasuresViewModel
        {
            CareerPlanningFormID = 1,
            ResultsMeasuresSections = new List<ResultsMeasuresSectionModel>
            {
                new ResultsMeasuresSectionModel
                {
                    SectionID = 1,
                    IsRequired = false,
                    IsSelected = true,
                    ActionPlanLabels = new List<ActionPlanLabelModel>
                    {
                        new ActionPlanLabelModel
                        {
                            LabelID = 1,
                            IsSelected = true,
                        }
                    },
                    CanRepeat = false
                },
                new ResultsMeasuresSectionModel
                {
                    SectionID = 2,
                    IsRequired = false,
                    IsSelected = true,
                    ActionPlanLabels = new List<ActionPlanLabelModel>(),
                    CanRepeat = true,
                    RepeatNumberOfOccurrences = 2
                }
            }
        };
        var cpf = new CareerPlanningForm
        {
            CareerPlanningFormID = 1,
            SelectedResultsMeasuresSections = new EntitySet<SelectedResultsMeasuresSection>()
        };
        this.repository.GetCareerPlanningFormByID(model.CareerPlanningFormID).Returns(cpf);

        // Act
        this.target.SaveSelectedResultsMeasures(model);

        // Assert
        this.repository.Received(8).Commit();
        Assert.AreEqual(2, cpf.SelectedResultsMeasuresSections.Count);

        Assert.AreEqual(1, cpf.SelectedResultsMeasuresSections.Where(o => o.ResultsMeasuresSectionID == 1).Single().SelectedActionPlanLabels.Count());
        Assert.AreEqual(1, cpf.SelectedResultsMeasuresSections.Where(o => o.ResultsMeasuresSectionID == 1).Single().ResultsMeasuresSectionOccurrences.Count());

        Assert.AreEqual(0, cpf.SelectedResultsMeasuresSections.Where(o => o.ResultsMeasuresSectionID == 2).Single().SelectedActionPlanLabels.Count());
        Assert.AreEqual(2, cpf.SelectedResultsMeasuresSections.Where(o => o.ResultsMeasuresSectionID == 2).Single().ResultsMeasuresSectionOccurrences.Count());
    }
}

If there is anything else I can provide that will help, let me know.

Answer 1

It looks like you need to add ResultsMeasures to the ResultsMeasuresSections you're returning in the test?

Before you go further along that path though, it looks like you're doing a lot of work to simulate the behaviour of LINQ-to-SQL. I'd suggest dropping the unit tests that test the specific mechanics of what the code does, and switch to a test that hits a real or in-memory database to make sure your code has the behaviour you want. For example, given you've saved results measures for a CPF, make sure retrieving that CPF has the information you require.

The downside with testing things like .Received(8).Commit() is that you are testing against how you know/expect the other system to behave, not whether the code is actually behaving as required. I feel it is the latter point that is most valuable to us when testing.