Moq with Task await

Question

Since I have converted my WCF methods to Async, my unit tests have failed, and I can't figure out the correct syntax to get them to work.

Cllient proxy class

 public interface IClientProxy
{
     Task DoSomething(CredentialDataList credentialData, string store);
}

service class

  public class CredentialSync : ICredentialSync
{
    private ICredentialRepository _repository;

    private IClientProxy _client;

    public CredentialSync()
    {
        this._repository = new CredentialRepository();
        this._client = new ClientProxy();
    }

    public CredentialSync(ICredentialRepository repository, IClientProxy client)
    {
        this._repository = repository;
        this._client = client;
    }

   public async Task Synchronise(string payrollNumber)
    {
        try
        {
            if (string.IsNullOrEmpty(payrollNumber))
            {
                .... some code
              }
            else
            {
                CredentialDataList credentialData = new CredentialDataList();
                List<CredentialData> credentialList = new List<CredentialData>();

                // fetch the record from the database
                List<GetCredentialData_Result> data = this._repository.GetCredentialData(payrollNumber);
                var pinData = this._repository.GetCredentialPinData(payrollNumber);

                // get the stores for this employee
                var storeList = data.Where(a => a.StoreNumber != null)
                    .GroupBy(a => a.StoreNumber)
                    .Select(x => new Store { StoreNumber = x.Key.ToString() }).ToArray();

                var credential = this.ExtractCredentialData(data, pinData, payrollNumber);

                credentialList.Add(credential);
                credentialData.CredentialList = credentialList;

                foreach (var store in storeList)
                {       
                  //this line causes an Object reference not set to an instance of an object error
                   await  _client.DoSomething(credentialData, store.StoreNumber);

                }
            }
        }
        catch (Exception ex)
        {
            throw new FaultException<Exception>(ex);
        }
    }

Test Class

 /// </summary>
[TestClass]
public class SynchTest
{

    private Mock<ICredentialRepository> _mockRepository;
    private Mock<IClientProxy> _mockService;

    [TestInitialize]
    public void Setup()
    {
       ... some setups for repository which work fine
    }

[TestMethod]      
    public async Task SynchroniseData_WithOneEmployee_CallsReplicateService()
    {
        this._mockService = new Mock<IClientProxy>();
        this._mockService.Setup(x=>x.DoSomething(It.IsAny<CredentialDataList>(), It.IsAny<string>()));
        // arrange
        string payrollNumber = "1";
        CredentialSync service = new CredentialSync(this._mockRepository.Object, this._mockService.Object);

        // act
        await service.Synchronise(payrollNumber);

        // assert                 
        this._mockService.VerifyAll();
    }

The error is when ClientProxy.DoSomething is called:

Object reference not set to an instance of an object

The parameters are both fine.

If I convert my ClientProxy.DoSomething method to a synchronous method (public void DoSomething(...) )the code works fine, but I do need this to be called asynchronously

score 122 · Accepted Answer · edited Apr 01 '19 at 20:09

122

DoSomething returns null instead of returning a Task, and so you get an exception when awaiting it. You need to specify when building the mock that it should return a Task.

In this case it seems that you can simply return an already completed task using Task.FromResult so the mock setup should look like this:

this._mockService.Setup(...).Returns(Task.FromResult(false));

Beginning with the next version of .Net (4.6) you can use Task.CompletedTask like this:

this._mockService.Setup(...).Returns(Task.CompletedTask);

edited Apr 01 '19 at 20:09

Diego Osornio

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answered Feb 18 '15 at 10:43

i3arnon

113,022
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It should be noted in this case, false is just a placeholder, the value false is actually ignored by the mock, it just needs a task, any task, to complete. It could just as easily be "foo" instead of false... – mcse3010 Oct 18 '16 at 15:25
@mcse3010 indeed. – i3arnon Oct 18 '16 at 16:49
4

Upvoted for the 4.6 syntax, very concise and indicative of what it actually is. – starmandeluxe Sep 21 '17 at 06:52

score 34 · Answer 2 · answered Jul 08 '16 at 18:56

34

You can reduce the amount of clutter in the code by using ReturnsAsync

this._mockService.Setup(...).ReturnsAsync(false);

This way you can remove the Task.FromResult part of the code

answered Jul 08 '16 at 18:56

knorman

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score 6 · Answer 3 · edited Apr 01 '19 at 20:28

6

I think you need to return the Task from the DoSomething mock

this._mockService.Setup(x => x.DoSomething(It.IsAny<CredentialDataList>(), It.IsAny<string>()))
    .Returns(Task.FromResult<int>(0));

edited Apr 01 '19 at 20:28

Johnny

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answered Feb 18 '15 at 10:43

NeddySpaghetti

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Or my favorite is `.Returns(Task.Delay(0));` – Michael Plautz Feb 23 '18 at 08:39

Moq with Task await

3 Answers3

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