I agree they might be necessary sometimes, but if they are necessary, they are a sign of a bad system.
This is only a problem in the USA, because of wildly varying quality of college and university programs. In most advanced countries, where education is more centralized, a biology degree at any university would guarantee high standards. So the first step would be start stripping crappy universities and colleges of the right to grant degrees, until all US universities (not just the Ivy League and top tier of State universities) were up to the standard of universities in France, Britain, Germany, Canada, Australia, Israel, etc. Then you wouldn’t need to administer any post-graduation tests to science teachers, or history teachers, or English teachers, or anybody else.
But this means that the notion of “failure” has to be reintroduced into the system. If 15-20% of college science students aren’t failing the science programs, it’s probably because the science programs are too easy. The degree has to be made so hard that only good students can get through it. Then the school system, in hiring science grads, would know it was hiring competent ones. And the same should be done in English, History, etc. Probably 40% of college students write so badly and read with such little comprehension that they have no hope of benefiting from a Humanities B.A., so it would be better to flunk those ones out, to make sure they don’t later on become English or history teachers and contaminate the high schools.
There has to be a will to excellence, or the system will never improve. The 1960s idea that every American has the right to life, liberty, and the pursuit of at least a Master’s, has to be abandoned. Only a minority of the population will ever be academically talented, and those are the ones who should get the degrees and become the history, English, geography, language, and science teachers in the schools (if they don’t become doctors, lawyers, scientists, etc.). The others should take up careers in industry, sales, business, sports, crafts, entertainment, social services, etc.