Checking the expected valued passed to a delegate using Rhino.Mocks

Question

I am attempting to write a test case that will confirm that the value of a parameter passed into the method under test was used to invoke a delegate function that is passed as an argument to a method on a mocked service. The example below illustrates what I am doing:

The method under test:

public IList<IResultData> GetResultData(int id)
{
    Func<IExternalInterface, List<ExternalData> getDataMethod = client => client.GetExternalData(id);     
    List<ExternalData> externalDataList = serviceClient.ExecuteService(getDataMethod, "GetExternalData"); 

    var result = new List<ResultData>();

    //Some code to convert externalDataList into an IList<IResultData>

    return result;
}

The test method:

[TestMethod]
public void TestMethodCall()
{
    var mockServiceClient = MockRepository.GenerateMock<IServiceClient>();
    mockServiceClient.Expect(x => x.ExecuteService(
            Arg<Func<IExternalInterface, List<ExternalData>>.Is.NotNull,
            Arg<string>.Is.Equal("GetExternalData")));

    var myClass = new MyClass(mockServiceClient);

    var result = myClass.GetResultData(3);

    //Some assertions that result is as expected.
}

Is there a way to assert that the function passed into the Execute method is being passed the id of 3 from the test method's call to GetResultData()? The service being mocked is in a library not under my control so I can't change it's signature.

Answer 1

The following pattern will allow you to assert the lambda:

[TestMethod]
public void TestMethod1()
{
    var wasCalled = false;

    var fakeService = MockRepository.GenerateStub<IExternalInterface>();

    fakeService.Stub(x => x.GetExternalData(1))
               .Return(new List<ExternalData>() {new ExternalData() {Id = 1}});

    fakeService.Stub(service => service.ExecuteService(Arg<Func<IExternalInterface, 
                     List<ExternalData>>>.Is.Anything, Arg<string>.Is.Anything))
               .WhenCalled(invocation =>
               {
                   wasCalled = true;
                   var func = (Func<IExternalInterface, List<ExternalData>>) invocation.Arguments[0];
                   var res = func(fakeService);

                   //
                   // Assert here the "res"
                   //


               }).Return(null);

    var target = new MyClass(fakeService);

    target.GetResultData(1);

    Assert. IsTrue(wasCalled);
}

However based you the code you've provided a better solution would be to use Do method as the following:

[TestMethod]
public void TestMethod1()
{
    var fakeService = MockRepository.GenerateStub<IExternalInterface>();

    fakeService.Stub(x => x.GetExternalData(1)).Return(new List<ExternalData>() {new ExternalData() {Id = 1}});

    fakeService.Stub(service => service.ExecuteService(Arg<Func<IExternalInterface, 
                                                       List<ExternalData>>>.Is.Anything, Arg<string>.Is.Anything))
               .Do(new Func<Func<IExternalInterface, List<ExternalData>>, string, List<ExternalData>>((func, str)=>func(fakeService)));

    var target = new MyClass(fakeService);

    var result = target.GetResultData(1);

    //
    // Assert here the "result"
    //

}