How does QA verify that existing product functionality is still working while verifying new product features and functionality?

How does QA verify that ex开发者_开发技巧isting product functionality is still working while verifying new product features and functionality?

Normally, you would employ unit tests to arrange for some sort of regression testing. Other than that, this is hardly possible.

Regression Testing. Partly automated, partly manual, depending on the tools, time and money.

Normally you should different levels of testing, and even though as software developers we would like to automate everything, some things have to be verified by hand, by having a collection of test cases executed by testers.

The Wikipedia article on regression testing is a good read.

From the whole collection of tests that most be checked by hand, it is normally worthwhile to select the minimum set that guarantee the functionality of the system to reduce costs. The balance, of course, is a fine one and depends a lot on how much the code was actually changed. Good modularization of the software product helps a lot on having good regression testing.

I read up quite a lot about testing, found an excellent resource on tripod (of all places). I will just link to it so other people can benefit from it also. Look under What is software Testing..? It's clearly outlined to answer the "majority" of questions you might have.

http://bazman.tripod.com

The other main way to verifiy existing functionality is to have automated integration and system level test/s, in addition to unit testing as pointed out by @Developer Art. These will catch problems in the interfaces between system components that unit tests are liable to miss.

The Wikipedia entry on test automation is a good introduction to the topic.