Mock a method of the subject under test in Moq?

Question

I want to test method A of my class, but without calling the actual method B which is normally called by A. That\'s because B has a lot of external interactions I don\'t want to

Answer 1

It is, with a catch! You have to make sure method B is virtual and can be overriden.

Then, set the mock to call the base methods whenever a setup is not provided. Then you setup B, but don't setup A. Because A was not setup, the actual implementation will be called.

var myClassMock = new Mock<MyClass>();
myClassMock.Setup(x => x.B()); //mock B

myClassMock.CallBase = true;

MyClass obj = myClassMock.Object;
obj.A(); // will call the actual implementation
obj.B(); // will call the mock implementation

Behinds the scenes, Moq will dynamically create a class that extends MyClass and overrides B.