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    While it is not immediately obvious to most people when they start thinking about doing test metrics for the first time, it just as important to monitor for performance improvement as it is to watch for degradation. If the execution time of a test unexpectedly goes down and the test still passes, it may be that some upstream developer has quietly done an optimization somewhere, or it may be an indication that some aspect of the action under test isn’t happening correctly anymore and the test isn’t detecting the failure. Either way, you’ve got an issue to diagnose, just as if the execution time had suddenly increased.