ITPEC FE Morning October 2023 Question 46
The integration test for software composed of modules arranged in a hierarchical structure is performed from a high-level module. In such a case, which of the following is a test module that is used as a substitute for a low-level module?
Explanation
Stub — in top-down integration testing, a stub stands in for a lower-level module that is not yet available.
Top-down integration starts from the highest-level module. The modules it calls may not be written or tested yet, so each one is replaced by a stub: a simple dummy module that accepts the call and returns a fixed or minimal result. As real lower modules are finished, they replace the stubs one by one.
The opposite approach, bottom-up integration, starts from low-level modules and needs a driver, a dummy higher-level module that calls the module under test and passes it test data.
Answer (d)
Why not others:
- •(a) Driver — substitutes an upper, calling module; it is used in bottom-up testing
- •(b) Emulator — imitates a whole hardware or software environment so programs can run on another platform; it is not a module substitute
- •(c) Simulator — models the behaviour of a system or device for experiments or training, not a placeholder for one module
Key rule: Stubs are called (they replace the level below); drivers call (they replace the level above).
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