In Component Testing, we test those test objects which are separately testable as an isolated unit without integrating with other components.
Component testing is also known as module and program testing. It finds the defects in the module and verifies the functioning of the software. This testing generally performed by the Testers.
Component testing is done in isolation from rest of the system depending on the SDLC model chosen for that particular application. In such case we need driver and stub to play the role of supported missing components, So missing software is replaced by Stubs and Drivers and simulate the interface between the software components in a simple manner.
Stubs : Stubs are considered as the dummy modules that always stimulate the low-level modules. Stubs are dummy modules that are always distinguish as “called programs”, or you can say that is handled in integration testing (top-down approach), it used when sub programs are under construction.
Driver : Drivers are considered as the dummy modules that always simulate the high-level modules. A driver calls the component to be tested. Drivers are also considered as the form of dummy modules which are always distinguished as “calling programs”, that is handled in the bottom-up integration testing, it is only used when main programs are under construction.