The purpose of the discipline.
WHAT TESTING DOES
Provides information about whether software behaves as intended.
WHAT IT DOES NOT DO
Prove software is correct.
WHY NOT
The number of possible inputs and states is effectively infinite, so testing samples rather than exhausts.
WHAT FOLLOWS FROM THAT
Testing reduces risk; it does not eliminate it.
WHAT THE REAL QUESTION IS
Whether the remaining risk is acceptable.
WHAT THAT MAKES TESTING
A business decision informed by technical work, not a technical activity alone.
WHAT QUALITY ASSURANCE MEANS
Building processes that prevent defects.
WHAT QUALITY CONTROL MEANS
Detecting defects in what was built.
WHY THE DISTINCTION MATTERS
Prevention is cheaper than detection, and detection is cheaper than repair after release.
WHAT THE COST CURVE LOOKS LIKE
A defect found while writing costs minutes Found in testing, hours Found in production, days and reputation
WHAT THAT ARGUES FOR
Finding defects as early as possible.
WHAT TESTING ALSO PROVIDES
Confidence to change code Documentation of intended behaviour A record of what was verified
WHAT TO MEASURE
Whether defects reach users, not how many tests exist.
