All tests are open to this kind of uncritical abuse. Since there are so many facets of cognitive ability, it is obvious that no test can be an adequate measure of them all. Only full knowledge of the items can reveal what is being measured. Furthermore, the testing situation may completely change the expected behavior. A test producer's claims for an achievement test or an aptitude test do not mean that it will function as such in all circumstances with all pupils.
Every test score contains an error of measurement.
It is a misuse of any test score or any observation to accept it as a fixed, unchanging index containing no error. It does mean that the test score is being misused if knowledge of the size of the errors of measurement is not used in interpreting the score. In the case of most standardized test scores, the magnitude of the errors is made explicit, not hidden or unknown. In fact, the errors in essay grading or any other type of evaluative data have far larger but usually unknown errors of measurement. Some people reject the notion of basing decisions on probabilistic data.