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As we discussed before software development efforts normally result

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in the delivery of a software product that satisfies

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the user requirements. So normally our software development organization

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will release this application to its final users, however, once

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the software is in operation many things can happen.

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So, for example, the environment might change. There might be

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new libraries. There might be new systems in which

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our software has to operate. Or they may be future

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requests, so the users may find out that, guess what,

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they want to do something different with the problem that

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we gave them. Or, again, and this is one of

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the most common occurrences, users might find problems with the

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software and may file bug reports and send the bug

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reports back to the software developer. These are the reasons

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why software maintenance is a necessary phase in software development.

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Software maintenance is the activity that sustains the software product

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as it evolves throughout its life cycle, specifically

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in response to bug reports, feature requests and

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environment changes. Development organisations perform three kinds of

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maintenance activities: corrective maintenance to eliminate problems with the

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code, perfective maintenance to accommodate feature request, and

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in some cases just to improve the software, for

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example, to make it more efficient, and finally,

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adaptive maintenance, to take care of the environment changes.

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And after this activities have been performed, the software developer

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will produce a new version of the application, will release it

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and the cycle will continue through out the lifetime of

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the software. That's why maintenance is a fundamental activity and a

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very expensive one. And one of the reasons why maintenance

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is expensive, that I want to mention now, is regression testing.

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During maintenance every time you modify your application you have

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to regression test the application, where regression testing is the activity

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of retesting software after it has been modified to make sure

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that the changes you perform to the software work as expected,

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and that your changes did not introduce any unforseen effect. I'm

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pretty sure that you're familiar with the case of a new

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version of the software being released and just a couple of

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days later another version being released to fix some problems that

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occor with the new version. These problems is what we call

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regression errors and they're what regression

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testing targets and tries to eliminate

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before the new version of the software is released into the world.