Here’s the setup:

You have a project that uses NUnit 2.5.5. You don’t actually have NUnit installed - you have it checked in along with your project’s source as a third-party dependency. (You did it that way so you can have different projects using different NUnit versions without having to install/uninstall things.) You’re using TestDriven.NET to run tests inside Visual Studio but you noticed that it ships with NUnit 2.5.3 - an earlier version of NUnit - and you want to use the version your project references.

How do you tell TestDriven.NET to use your project’s version of NUnit?

First, make sure your checked-in version of NUnit keeps the same directory structure it’s distributed with. That means you have a folder that contains the appropriate version of NUnit-Console.exe, etc., and a subfolder called “framework” that has the nunit.framework.dll in it, like this:

YourProject
|
+-lib
  |
  +-NUnit // Has NUnit-Console.exe in it
    |
    +- framework // Has nunit.framework.dll in it
    |
    +- lib
    |
    +- tests

Ensure you’re referencing nunit-framework.dll from the NUnit “framework” folder. There’s an nunit.framework.dll in the NUnit folder, probably, too, but don’t reference that one - reference the one in the “framework” folder.

Open the TestDriven.NET install folder. This will be something like C:\Program Files\TestDriven.NET 3. On a 64-bit system it might be in C:\Program Files (x86)\TestDriven.NET 3 or the like.

Go into the TestDriven NUnit folder for the version you’re referencing. You should see a folder called “NUnit” in the TestDriven.NET install folder. Open that. Inside there you’ll see different folders for each version of NUnit. Right now there’s “2.2,” “2.4,” and “2.5.” In this example, we’re looking at using NUnit 2.5.5 instead of 2.5.3, so we’ll open up the “2.5” folder. You should now be in a folder like C:\Program Files\TestDriven.NET 3\NUnit\2.5.

Copy the nunit.tdnet.dll file into your lib\NUnit folder. Look in the TestDriven.NET NUnit version folder you should be in right now. You’ll see a file called “nunit.tdnet.dll.” Copy that into your checked-in lib\NUnit folder - the same folder that has NUnit-Console.exe in it. You will need to check this in along with your NUnit dependency.

Go into the TestDriven.NET “framework” folder. Still in that C:\Program Files\TestDriven.NET 3\NUnit\2.5 folder - open the “framework” folder under that. You should be in C:\Program Files\TestDriven.NET 3\NUnit\2.5\framework.

Copy the nunit.framework.dll.tdnet file into your lib\NUnit\framework folder. In that C:\Program Files\TestDriven.NET 3\NUnit\2.5\framework folder you should see a file called “nunit.framework.dll.tdnet”. Copy that into your lib\NUnit\framework folder - the same folder that has nunit.framework.dll in it. You will need to check this in along with your NUnit dependency.

Run TestDriven.NET. Now when you run your tests with TestDriven.NET you should see it report that it’s using the version of NUnit you have checked in along with your project. That wasn’t too hard, now, was it?

What if I need to customize the locations? What if you don’t have the whole NUnit/framework folder structure and such? The basic principle here is that nunit.tdnet.dll needs to be in the same folder as NUnit-Console.exe and nunit.framework.dll.tdnet needs to be in the same folder as nunit.framework.dll. You may need to open the nunit.framework.dll.tdnet file in a text editor (it’s an XML file) and modify the “AssemblyPath” node in there. I haven’t actually tried this myself, so YMMV, but it should work.