NUnit is an open source unit testing framework for Microsoft .NET and Silverlight written in C#. It serves the same purpose as JUnit does in the Java world, and is one of many in the xUnit family.
Initially ported from JUnit, the current production release, version 2.6, is the seventh major release of this xUnit based unit testing tool for Microsoft .NET. It is written entirely in C# and has been completely redesigned to take advantage of many .NET language features, for example custom attributes and other reflection related capabilities. NUnit brings xUnit to all .NET languages.