Paulo Morgado

Improving Debugging And Testing Through Assertions

Reading through the The Typemock Insider blog, I came across this post from Gil Zilberfeld.

I myself tend to fall in Gil’s practice ("binary search" debugging), but I don’t think Kent Beck has the right solution.

Gil’s suggestion of using Isolator is tempting (I don’t miss an opportunity to use it), but still not my favorite one.

I prefer to use debug assertions. Debug assertions can be used when running a debug version of the application to pop-up assertion messages and when running unit tests to fail tests.

In order to use debug assertions in unit tests a “special” trace listener is needed to make the test fail when its Fail method is called.

public class UnitTestTraceListener : global::System.Diagnostics.DefaultTraceListener
{
     public UnitTestTraceListener() : base()
    {
        this.Name = "UnitTest";
        this.AssertUiEnabled = false;
    }

    public override void Fail(string message, string detailMessage)
    {
        Microsoft.VisualStudio.TestTools.UnitTesting.Assert.Fail("Debug.Assert Failed: " + message + " " + detailMessage);
    }
}

Now, all you need to do is register it.

Registering the trace listener can either be done in code:

System.Diagnostics.Trace.Listeners.Remove("Default");
System.Diagnostics.Trace.Listeners.Add(new UnitTestTraceListener());

or configuration:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.diagnostics>
    <assert assertuienabled="false"/>
    <trace>
      <listeners>
        <clear/>
        <add name="UnitTest" type="UnitTestTraceListener"/>
      </listeners>
    </trace>
  </system.diagnostics>
</configuration>

And if I’m using Isolator I have the take in account the accesses made in the call to the Assert method. More fun to me.