Top down integration testing we have 3 modules A,
B and C. say A and B are ready but C. But A and B calls
functions from C. In this case, to proceed with the testing
a dummy code is written to work as C. This function/code is
called a Stub.

Same way in Bottom up testing Say A, B are ready but C is
not. And C has to return value to A and B. For this a dummy
code is written to return a vale. This is called Driver.

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- Drivers and stubs are a part of incremental testing.

- The two approaches used in incremental testing are: the top down and the bottom up methods.

- Drivers are used for the bottom up approach.                            

- Drivers are the modules that run the components that are being tested.

- A stub is used for the top down approach.

- It is a replacement of sorts for a component which is used to test a component that it calls.

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