使用NUnit使用异步/等待方法进行单元测试

Question

We recently updated our entire solution to Framework 4.5.2 and are using async/await. I have written several tests already for the data services layer and part of the business services layer, but I now have a new test that fails with NUnits' "not all expected invocations were performed". We are using NUnit V3.0.1 and NMock 2.0.0.

This is the method under test:

public async Task<objQuote> RetrieveQuoteAsync(int quoteid)
    {
        var q = await _data.RetrieveQuoteAsync(quoteid);
        if (q != null)
        {
            q.Milestones = await _data.RetrieveAllMilestonesForQuoteAsync(quoteid);
            q.Assignments = await _data.RetrieveAssignmentsForQuoteAsync(quoteid);
        }
        return q;
    }

And this is the definition for the data class being mocked (_data in the above code):

public interface IQuotesData
{
    string ConnectionString { get; set; }


    Task<int> SaveQuoteAsync(objQuote quote);

    Task<objQuote> RetrieveQuoteAsync(int quoteid);

    //objQuote RetrieveQuoteWithoutAssignments(int quoteid);

    Task<List<objQuote>> RetrieveAllQuotesAsync();

    Task<List<objQuote>> RetrieveAllQuotesForFYAsync(int fy);

    Task<int> SaveQuoteActivityAsync(objQuoteActivity qa);

    Task DeleteQuoteAsync(int quoteid);

    Task<int> SaveQuoteMilestoneAsync(objQuoteMilestone ms);

    Task<List<objQuoteMilestone>> RetrieveAllMilestonesForQuoteAsync(int quoteid);

    Task<List<objQuoteActivity>> RetrieveAllQuoteActivitiesAsync(int quoteid);

    Task<int> SaveAssignmentAsync(objAssignment ass);

    Task<int> SaveAssignmentOverheadAsync(objFAOverHead oh);

    Task<List<objFAOverHead>> RetrieveAllOverheadsForAssignment(int assignmentid);

    Task<objAssignment> RetrieveAssignmentAsync(int assid);

    Task<List<objAssignment>> RetrieveAssignmentsForQuoteAsync(int quoteid);

    Task<int> SaveDelegationAsync(objDelegation del);

    Task<int> SaveDelegationOverheadAsync(objFAOverHead oh);

    Task<List<objFAOverHead>> RetrieveAllOverheadsForDelegation(int delegationid);

    Task<List<objDelegation>> RetrieveDelegationsforAssignment(int assid);

    Task<int> SaveCommentAsync(objQuoteComment comment);

    Task<List<objQuoteComment>> RetrieveAllCommentsForQuoteAsync(int quoteid);
}

And this is my Test:

 [Test]
    public async void Can_Retrieve_Quote()
    {
        const int quoteid = 42;
        var quote = new objQuote() { ID = 42};
        var msList = new List<objQuoteMilestone>();
        var assignmentList = new List<objAssignment>();

        Expect.Once.On(_data).Method("RetrieveQuoteAsync").With(Is.EqualTo(quoteid)).Will(Return.Value(quote));
        Expect.Once.On(_data).Method("RetrieveAllMilestonesForQuoteAsync").With(Is.EqualTo(quoteid)).Will(Return.Value(msList));
        Expect.Once.On(_data).Method("RetrieveAssignmentsForQuoteAsync").With(Is.EqualTo(quoteid)).Will(Return.Value(assignmentList));

        var biz = new QuotesBiz(_data, _empData, _logger, _mailer);
        Assert.IsNotNull(biz);
        var results = await biz.RetrieveQuoteAsync(quoteid);
        Assert.That(results != null);

    }

At this point I'm not sure if it's a coding problem or a testing problem. It appears that the two calls inside the "if" statement of the code under test are not being executed.

TIA to anyone that can help figure this out.

Answer 1

From within the method being tested the methods that you are calling on the mock are expecting a Task to be returned where your mock is returning the concrete object instead.

I don't have any experience with NMock specifically but I know other mocking libraries will fail silently when the type of the object you specify to return does not match that of the method being called.

To solve this you can use the static method Task.FromResult like so:

[Test]
public async void Can_Retrieve_Quote()
{
    const int quoteid = 42;
    var quote = new objQuote() { ID = 42};
    var msList = new List<objQuoteMilestone>();
    var assignmentList = new List<objAssignment>();

    Expect.Once.On(_data).Method("RetrieveQuoteAsync").With(Is.EqualTo(quoteid)).Will(Return.Value(Task.FromResult(quote)));
    Expect.Once.On(_data).Method("RetrieveAllMilestonesForQuoteAsync").With(Is.EqualTo(quoteid)).Will(Return.Value(Task.FromResult(msList)));
    Expect.Once.On(_data).Method("RetrieveAssignmentsForQuoteAsync").With(Is.EqualTo(quoteid)).Will(Return.Value(Task.FromResult(assignmentList)));

    var biz = new QuotesBiz(_data, _empData, _logger, _mailer);
    Assert.IsNotNull(biz);
    var results = await biz.RetrieveQuoteAsync(quoteid);
    Assert.That(results != null);

}

In the future you can catch issues like these by debugging the test an inspecting what your mocks are returning, in this case you would see a null.