There are several great mocking frameworks available for .Net, but NSubstitute stands out because of its simple and elegant syntax. Perhaps the biggest benefit is how easy it is to integrate mocked objects with the code under test. There is no need for framework specific bootstrapping, or extra properties to access the objects you are mocking. A pure virtual class is defined as one with all its public methods and properties defined as virtual or abstract and with a default, parameterless constructor defined as public or protected. ... The syntax for NSubstitute is a little different than the others. In most cases, there's not an explicit method you call to create the mock/stub. 1. public class MyClassMock : MyClass. You can now test the behaviour on MyClass, via MyClassMock; however, you still can't* override the method ReadNumberOfRowsInFileOnDisk () because it isn't virtual. If you make the method virtual, you can override it in the subclass. The same is true with NSubstitute - if you want to partially mock a.