Nunit and standard assertion

2008, Jun 03 2 mins read

If you use Nunit and use standard System.Diagnostics.Debug.Assert in your code, you can get tired of the messagebox that is raised when a standard assertion fail. To avoid this, you can use app.config to completely remove all listener during the test.

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    <system.diagnostics>
         <trace autoflush="false" indentsize="4">
             <listeners>
                 <clear/>
             </listeners>
         </trace>
     </system.diagnostics>

This solves the problem, now you can launch nunit interface, run the test and get rid of the annoying messagebox that gets displayed when a standard assertion fail. If you do not want to use app.config, you can still create a base test class, and clear the listeners in the fixture setup.

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readonly List<TraceListener> oldListener = new List<TraceListener>();
[TestFixtureSetUp]
public void FixtureSetup() {
    foreach (TraceListener listener in Trace.Listeners)
        oldListener.Add(listener);
    Trace.Listeners.Clear();
}
[TestFixtureTearDown]
public void FixtureTearDown()
{
    Trace.Listeners.AddRange(oldListener.ToArray());
}

With this code you get the same effect, except that now you can disable listeners per test instead of disabling for entire test suite.

This technique has a drawback, in this way you completely disable standard assertions, but I like that my tests fail even if a standard assertion fails, and it is good to make possible for me to choose if in a test I want that standard assertion make my test fail or not. A quick and dirty solution is the following

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public class NunitTraceListener : TraceListener
{
    public override void Fail(string message)
    {
        NUnit.Framework.Assert.Fail("StandardAssertionFailed: " + message);
    }

    public override void Fail(string message, string detailMessage)
    {
        NUnit.Framework.Assert.Fail("StandardAssertionFailed: " + message);
    }
    public override void Write(string message)
    {
        Console.Write(message);
    }

    public override void WriteLine(string message) {
        Console.WriteLine(message);
    }
}

This class inherits from standard TraceListener, standard messages goes to the console (nunit is able to intercept them) and I override the two Fail() method that are called when some assert is failing. In my fail routines I simply make a standard fail assertion of nunit framework, this makes my test fail. The only thing you need to do is to set this listener in the trace.listeners collection

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readonly List<TraceListener> oldListener = new List<TraceListener>();
[TestFixtureSetUp]
public void FixtureSetup()
{
    foreach (TraceListener listener in Trace.Listeners)
        oldListener.Add(listener);
    Trace.Listeners.Clear();
    Trace.Listeners.Add(new NunitTraceListener());
}
[TestFixtureTearDown]
public void FixtureTearDown()
{
    Trace.Listeners.Clear();
    Trace.Listeners.AddRange(oldListener.ToArray());
}

alk.

Tags: nunit TraceListener