Essentially, the test driver mimics the components of a system that interact with the component under test, feeding it the necessary input and controlling its execution.
The primary goal of using a test driver is to verify the functionality of the isolated component in the absence of its intended complete environment.
With manual test drivers, testers can directly initiate actions, offering them direct control throughout the testing phase.
These are especially useful in situations that demand repetitive or extensive testing.
Test drivers are typically an active component and control or call the system under test without further inputs after they are initialised, stubs on the other hand are usually passive components that only receive data and respond to calls from the tested system when needed.