xUnit versus NUniut versus MSTest

xUnit:

xUnit.net is a free, open source, community-focused unit testing tool for the .NET Framework. xUnit has an impressive list of extensions which other testing frameworks are lacking. xUnit uses intuitive terminology and is frequently updated to be more lean and user-friendly.

Xunit is 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 is becoming quite popular and is fully compatible with ASP.NET 5 / vNext / CoreCLR. This means we can easily use xUnit in MVC6 projects to start adding unit tests. 

NUnit: NUnit is one of the most popular testing frameworks for .NET. Due to it’s popularity and active development, plenty of learning resources (such as detailed documentation and various tutorials) exist for learning NUnit.

NUnit is developed slowly; some developers complain that it is no longer able to keep up with new testing approaches.

MSTest: MSTest is fully integrated with Visual Studios and works natively without the need for any plugins. Last update was for Visual Studio 2010. Even Microsoft is migrating away from using it. MSTest is better suited for only using Microsoft technologies rather than mixed technology environments.