How are test drivers and test stubs used in the software quality assurance process?

"Test drivers and test stubs are two ways quality assurance engineers can test how different components within a software design interact with each other. These are especially helpful when one of the components has not been developed yet. A test stub is part of the code and is used in a top-down testing approach. On the other hand, the test driver is a piece of code that calls one of the software components and is used in a bottom-up approach. Both of these are important tools used by quality assurance engineers."