In unit testing terminology, there are several types of object that fall into the category named test doubles. A test double is a type of object that will take the place of a real one in our test suite for different kinds of reasons (maybe we don't need the actual production code, but just a dummy object would work, or maybe we can't use it because it requires access to services or it has side-effects that we don't want in our unit tests, and so on).
There are different types of test double, such as dummy objects, stubs, spies, or mocks. Mocks are the most general type of object, and since they're quite flexible and versatile, they are appropriate for all cases without needing to go into much detail about the rest of them. ...
