Isolating Code under Test with Microsoft Fakes
This article explains how Microsoft Fakes perform a similar role than mocking in unit testing, helping you to isolate the code you are testing in Visual Studio by replacing other parts of the application with stubs or shims. A stub replaces another class with a small substitute that implements the same interface. A shim modifies the compiled code of your application at run time so that instead of making a specified method call, it runs the shim code that your test provides.