NSubstitute
A friendly substitute for .NET mocking libraries
... frequently required operations obvious and easy to use, keeping less usual scenarios discoverable and accessible, and all the while maintaining as much natural language as possible. There are already some great mocking libraries around for .NET, so why create another? We found that for all their great features, none of the existing libraries had the succinct syntax we were craving — the code required to configure test doubles quickly obscured the intention behind our tests.