- Moq
- "Root namespace of Moq (pronounced "Mock-you" or just "Mock"), the only mocking library for .NET developed from scratch to take full advantage of .NET 3.5 (i.e. Linq expression trees) and C# 3.0 features (i.e. lambda expressions) that make it the most productive, simple and refactoring-friendly mocking library available."
http://www.clariusconsulting.net/labs/moq/index.html