Determine if code is running as part of a unit test

I have a unit test (nUnit). Many layers down the call stack a method will fail if it is running via a unit test.

Ideally you would use something like mocking to setup the object that this method is depending on but this is 3rd party code and I can't do that without a lot of work.

I don't want setup nUnit specific methods - there are too many levels here and its a poor way of doing unit test.

Instead what I would like to do is to add something like this deep down in the call stack

#IF DEBUG // Unit tests only included in debug build
if (IsRunningInUnitTest)
   {
   // Do some setup to avoid error
   }
#endif

So any ideas about how to write IsRunningInUnitTest?

P.S. I am fully aware that this is not great design, but I think its better than the alternatives.

Solution

I've done this before - I had to hold my nose while I did it, but I did it. Pragmatism beats dogmatism every time. Of course, if there is a nice way you can refactor to avoid it, that would be great.

Basically I had a "UnitTestDetector" class which checked whether the NUnit framework assembly was loaded in the current AppDomain. It only needed to do this once, then cache the result. Ugly, but simple and effective.