☛ The stub is called from the software component to be tested, it is used in top down approach

☛ The driver calls a component to be tested, it is used in bottom up approach

☛ It is required when we need to test the interface between modules X and Y and we have developed only module X. So we cannot just test module X but if there is any dummy module we can use that dummy module to test module X

☛ Now module B cannot receive or send data from module A directly, so in these case we have to transmit data from one module to another module by some external features. This external feature is referred as Driver