The test driver is a section of code that calls a software component under test. It is useful in testing that follows the bottom-up approach.
The test stub is a dummy program that integrates with an application to complete its functionality. It is relevant for testing that uses the top-down approach.
For example:
Let’s assume a scenario where we have to test the interface between Modules A and B. We have developed only Module A. Here, we can test Module A if we have the real Module B or a dummy module for it. In this case, we call Module B as the test stub.
Now, Module B can’t send or receive data directly from Module A. In such a scenario, we’ve to move data from one module to another using some external features called test driver.