How To Build an NUnit Addin

Since version 2.2.x of NUnit it was possible to build your own core extensions, but this feature was experimental. With the latest release Addins are officially supported. Core extensions can customize NUnit's internal behavior such as the creation of tests and their execution.

Writing an Addin

An Addin needs to implement the interface NUnit.Core.Extensibility.IAddin, which can be found in the assembly “nunit.core.interfaces”. Additionally the NUnit.Core.Extensibility.NUnitAddinAttribute must be applied to your Addin class. The attribute parameters Name and Description represent the name of the extension and a description of what it does. You can leave ExtensionType at its default value (ExtensionType.Core), because NUnit supports only core extensions by now. The interface NUnit.Core.Extensibility.IAddin has only one method which is called Install. Your Addin class will install extensions at certain extension points, places where the NUnit functionality can be extended. To locate such extension points your Addin class uses the extension host, which is passed as parameter. The Install method returns true when your Addin was able to install your extensions, otherwise it returns false. A minimal Addin would look like this:

using System;
using NUnit.Core.Extensions;

[NUnitAddin(Name=”MyAddin”,
    Description=”This Addin does not do anything.”)]
public class MyAddin : IAddin
{
  public bool Install(IExtensionHost host)
  {
    return true;
  }
}

How to Install an Addin

After compiling the Addin copy the assembly to the bin/addins directory relative to the NUnit install directory. Start the NUnit GUI and you should see your Addin listed under Tools -> Addins...: MyAddin does not do anything useful. The next time I'll show you how to write a test decorator.