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Bottom-Up Strategy

Glossary of Software QA/Testing

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Bottom-Up Strategy

Bottom-up approach, as the name suggests, is the opposite of the Top-down method.
This process starts with building and testing the low level modules first, working its way up the hierarchy.
Because the modules at the low levels are very specific, we may need to combine several of them into what is sometimes called a cluster or build in order to test them properly.
Then to test these builds, a test driver has to be written and put in place.
The advantage of Bottom-up integration is that there is no need for program stubs as we start developing and testing with the actual modules.
Starting at the bottom of the hierarchy also means that the critical modules are usually build first and therefore any errors in these modules are discovered early in the process.
As with Top-down integration, there are some drawbacks to this procedure.
In order to test the modules we have to build the test drivers which are more complex than stubs. And in addition to that they themselves have to be tested. So more effort is required.
A major disadvantage to Bottom-up integration is that no working model can be presented or tested until many modules have been built.

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