When a test fails even though the system under test (SUT) is working properly, the test is said to be giving a false positive indication or a "false failure". The terminology comes from statistical science when we try to calculate the probability of some observation error occuring. For example, in medicine we run tests to find out if a medical condition is present; if it is, the test is "positive". It is useful to know the probability of a test indicating that a condition (such a diabetes) is present when it is not; a false "positive". If we think of software tests as a way of determining whether a condition (a particular defect or bug) is present, a test that reports a defect (a test failure or error) when it is not in fact present is giving us a false positive.
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