What is the NUnit Framework?

NUnit framework is port of JUnit framework from java and Extreme Programming (XP).

This is an open source product. You can download it from http://www.nunit.org. The NUnit framework is developed from ground up to make use of .NET framework functionalities. It uses an Attribute based programming model. It loads test assemblies in separate application domain hence we can test an application without restarting the NUnit test tools. The NUnit further watches a file/assembly change events and reload it as soon as they are changed. With these features in hand a developer can perform develop and test cycles sides by side.

We should also understand what NUnit Framework is not:
1)It is not Automated GUI tester.
2)It is not a scripting language, all test are written in .NET supported language e.g. C#, VC, VB.NET, J# etc.
3)It is not a benchmark tool.
4)Passing the entire unit test suite does not mean software is production ready.