Consequential validity in testing describes the aftereffects and possible social and societal results from a particular assessment or measure. For an assessment to have consequential validity it must not have negative social consequences that seem abnormal. If this occurs it signifies the test isn't valid and is not measuring things accurately.
For example, a standardized test is given to an entire grade and a particular subgroup of students with shared traits all underperform in comparison to the other students. This can be a sign of invalidity. Why did all of the students with particular shared traits do worse? Possible reasons could be that the test was developed and written by members of the larger group.
Consequential validity can help identify tests that are not measuring things they are supposed to be measuring or that it is falsely measuring those actually taking it.