Unit testing WCF Faults

Question

What's the best way to unit test expected faults from WCF services?

I am attempting to unit test a WCF service which is (correctly) throwing FaultExceptions for a certain reproducible error. The unit tests get an instance of the WCF client and call the applicable service method, which throws a FaultException.

All of that works as you would expect, but I am having difficulty unit testing this, because the fault causes the IDE to break when the error isn't caught in the service implementation. Because I am using faults, and not exceptions, I was expecting the IDE to serialize the exception and send it to the client, where it would raise an exception.

I do see that there is a configuration option to disable breaking for specific user-unhandled exceptions, but I was hoping somebody could point out a better way to achieve the same results, as this isn't easily doable in a team environment.

Here's some sample code of what the implementation currently looks like...

The unit test project has a service reference to my WCF service, and I have defined the interface as such:

[OperationContract(Name = "DoSomething")]
[FaultContract(typeof(EpicFail))]
ResponseObject DoSomething(RequestObject requestObject);

The fault is defined as such:

[DataContract]
public class EpicFail
{

    public EpicFail(string action)
    {
        this.Reason = "Epic Fail";
        this.Action = action;
    }

    [DataMember]
    public string Reason
    {
        get;
        set;
    }

    [DataMember]
    public string Action
    {
        get;
        set;
    }

}

The code that calls the service looks vaguely like this:

[TestMethod()]
[ExpectedException(typeof(FaultException<EpicFail>))]
public void FaultTest_Fails_Epicly()
{
    bool testPassed = false;

    try
    {
        ResponseObject resp = GetServiceClient().DoSomething(req);
    }
    catch (FaultException<EpicFail>)
    {
        testPassed = true;
    }

    Assert.IsTrue(testPassed);
}

• I edited the code to show that I am using the ExpectedException attribute and it doesn't seem to be having much effect on keeping the IDE/Debugger from breaking when the exception is thrown in the service.

Answer 1

You can always use ExpectedExceptionAttribute (in NUnit) to make sure this is the exception thrown. MSTest has similar concept as well.

[ExpectedException(typeof(MyException))]
void my_test()
{
     // test
}

If you have some Mock verification to do, I would use try/catch block and verify in the catch and then throw the exception.

UPDATE

When you are using ExpectedException attribute, you are not supposed to catch the exception, instead you need to let the NUnit that runs your test to catch it.

If you need to verify special information in the exception then you catch the exception, verify the information and then rethrow:

[ExpectedException(typeof(MyException))]
void my_test()
{
     try
     {
         // call the service
     }
     catch(MyException ex)
     {
          Assert.IsTrue(ex.Message.Contains("error code 200"));
          throw ex;
     }

}

Answer 2

mattv,

Why does this test has to access the service remotely ? From what I see your code:

ResponseObject resp = GetServiceClient().DoSomething(req);

Is somehow getting a service client, and not a service instance itself. I'd advise to test the service concrete class directly for unit tests.

However, if you need this scenario, have you tried NOT CATCHING the exception and running the test? Does it give the same result?

And by the way, if you need to catch and rethrow use the following pattern:

try {
   //Do something
}
catch(SomeException e) {
   //Do something with e
   throw
}