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What does the principle 'tests wear out' mean, and what was it called earlier?
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In v4.0 the old 'pesticide paradox' was renamed 'tests wear out'. If the same tests are repeated many times, they become less effective at finding new defects because the code they exercise has already been fixed. Testers should modify existing tests and test data and write new tests. The exception is automated regression testing, where repeating the same tests is valuable because the goal is to confirm nothing has broken.