What is mock ? A mock is an object which we can use on behalf of another object. In short, mocking is creating (fake) objects that simulate the behavior of Real Objects. An object under test may have dependencies on other (complex) objects. To isolate the behavior of the object you want to test you replace the other objects by mocks that simulate the behavior of the real objects. When to mock ? Mocking is required when real objects are impractical to incorporate into the unit test. Most of the time external services or methods we have to mock. Once mocked, the