One problem with NUnit is it doesn’t necessarily test an application, but a library. This means that each test project is inherently an application, which needs a configuration file. NUnit’s way of looking for config files is a little odd, but according to this article, all it does is search for the DLL’s name with a .config extension in the output directory. Following the aforementioned article, creating a post build even to copy a config file from the project directory to the output directory solves this problem.