Fluentassertions : Fluent Assertions is a set of .NET extension methods that allow you to more naturally specify the expected outcome of a TDD or BDD-style test. We currently use it in all our internal and client projects, and it is used in many open-source projects. It runs on .NET 3.5, 4.0 and 4.5 (Desktop and Windows Store), Silverlight 4 and 5 and Windows Phone 7.5. And it supports the unit test frameworks NUnit, XUnit, MBUnit, Gallio and MSpec.
Source: Fluentassertions