Testing somebody on a test that correlates with IQ that correlates with technical ability that correlates with job performance is not okay, because of the levels of indirection passing through a very abstract space (a Bayesian coefficient of 'smartness'), which has historically been used discriminatorily against groups that it would otherwise be illegal to discriminate against.

Testing somebody on a test that correlates with technical skill that correlates with job performance (and maybe IQ) remains within the easy to defend realm of the concrete.