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Quality Assurance

The more you invest in quality, the less time it takes to develop working software.
Quality is not just testing
Trying to improve the quality of software by doing more testing is like trying to lose weight by weighing yourself more often. (Steve McConnell)

Quality is:

  • Designed in
  • Monitored and maintained through the whole software life cycle

This lecture looks at basic things every developer can do to maintain quality.

Limits to Testing

  • Suppose you have a function that compares two 7-digit phone numbers, and returns True if the first is greater than the second
  • 1072 possible inputs
  • At ten million tests per second, that's 155 days
  • If they're 7-character alphabetic strings, it's 254 years

o Then you move on to the second function…

  • And how do you know that your tests are correct?
  • All a test can do is show that there may be a bug

Nomenclature

A unit test exercises one component in isolation

  • Developer-oriented: tests the program's internals

An integration test exercises the whole system

  • User-oriented: tests the software's overall behavior

Regression testing is the practice of rerunning tests to check that the code still works

  • I.e., make sure that today's changes haven't broken things that were working yesterday
  • Programs that don't have regression tests are difficult (sometimes impossible) to maintain
software_carpentary2.1308541628.txt.gz · Last modified: 2018/03/24 11:13 (external edit)