In order to test an application under NUnit, you write test code that is specially annotated using custom Attributes. Your test code contains Assertions, which demonstrate the correct working of the application.
If your application stores settings in Configuration Files, NUnit provides you with the ability to have settings for your test, which are different from those used in production.
In addition to running tests in a single assembly, NUnit provides support for tests organized as Multiple Assemblies and for creating and running tests as NUnit Test Projects.
For those using NUnit on a Windows system with Visual Studio installed, Visual Studio Support is available.