NUnit is a unit-testing framework for all .Net languages. Initially ported from JUnit, the current production release, version 3.0, has been completely rewritten with many new features and support for a wide range of .NET platforms.
xUnit.net is a free, open source, community-focused unit testing tool for the .NET Framework. Written by the original inventor of NUnit v2, xUnit.net is the latest technology for unit testing C#, F#, VB.NET and other .NET languages. xUnit.net works with ReSharper, CodeRush, TestDriven.NET and Xamarin. It is part of the ASP.NET Open Source Gallery under the Outercurve Foundation, licensed under Apache 2 (an OSI approved license).