Define the term validity in evaluative testing.

In education, at least, the concept of test validity has
to do with whether the test truly measures what it is supposed to measure.  In other
words, if a test is supposed to measure a person's readiness for college and ability to
perform once they reach college, does the test really do
so?

Validity is an important consideration for those who
are writing tests, whether it be the SAT or the evaluations that a teacher uses on
students.  In  the case of the teacher, it is important that the questions on the test
should truly cover the material that was taught in the class.  In the case of the SAT,
it is important that test questions should actually measure the student's ability to do
college work (as opposed to measuring some set of prior knowledge that will not predict
college performance).

Validity in testing, then, is the
extent to which the test measures that which it is supposed to
measure.