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Bottom-Up Integration in Integration Testing

1. Low-level modules are combined into clusters that perform a specific software subfunction. These clusters are sometimes called builds.

2. A driver (a control program for testing) is written to coordinate test case input and output.

3. The build is tested.

4. Drivers are removed and clusters are combined moving upward in the program structure.

Fig. 9.7 (a) Program Modules (b)Bottom-up integration applied to program modules in (a)

Fig 9.7 shows the how the bottom up integration is done. Whenever a new module is added to as a part of integration testing, the program structure changes. There may be new data flow paths, some new I/O or some new control logic. These changes may cause problems with functions in the tested modules, which were working fine previously.

To detect these errors regression testing is done. Regression testing is the re-execution of some subset of tests that have already been conducted to ensure that changes have not propagated unintended side effects in the programs. Regression testing is the activity that helps to ensure that changes (due to testing or for other reason) do not introduce undesirable behavior or additional errors.

As integration testing proceeds, the number of regression tests can grow quite large. Therefore, regression test suite should be designed to include only those tests that address one or more classes of errors in each of the major program functions. It is impractical and inefficient to re-execute every test for every program functions once a change has occurred.

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