testing - What is Object Mocking and when do I need it?

Question

Many people use Mock Objects when they are writing unit tests. What is a Mock Object? Why would I ever need one? Do I need a Mock Object Framework?

Answer 1

Object Mocking is used to keep dependencies out of your unit test. Sometimes you'll have a test like "SelectPerson" which will select a person from the database and return a Person object.

To do this, you would normally need a dependency on the database, however with object mocking you can simulate the interaction with the database with a mock framework, so it might return a dataset which looks like one returned from the database and you can then test your code to ensure that it handles translating a dataset to a person object, rather than using it to test that a connection to the database exists.