Agile Testing Question:

A test stub is a bit of code that replaces an undeveloped or fully developed component within a system being tested. The test stub is built such that it mimics the actual component by generating specific known outputs. The stub can be used as a substitute for the actual (fully developed) component for testing purposes. The stub can also be used during testing to isolate system components and troubleshoot problems. A test stub is also known as a test double.