Then there are the pre-employment tests. The prospective employee
knows that
pre-employment testing is required. The prospective employee knows
that s/he
can decline or postpone the testing. Yet still, there are a few who
fail
pre-employment testing.

Are there? These people would have to be total idiots. Now, what is
more likely:
We have these total idiots applying for jobs, often with some pretty
impressive looking credentials, OR
The tests aren't quite as accurate as you think they are, and have a
fairly high false positive rate?

The question can be answered thus - what kind of GUARANTEE does the
drug testing operation give you? In other words, how much will they
pay in DAMAGES if they are wrong? If the answer is "a whole lot less
than a ruined career and reputation is worth" well, then, you have your
answer.

Michael