The scenario of indirection proposed (I didn't save the attribution)
for flushing out the drug dealers is just ducky.  I can see it now:
"We had a drug problem, and put in mandatory testing -- six people
left, and we have no problem anymore."  Anyone want to bet what
the inference will be, when those six interview for another job?
"You quit -Colonial Williamsburg- for a -principle-?  Yeah, sure."
And if the interviewer is of Holly Trimper's mindset, "If you had
nothing to hide, why'd you quit?"
 
--bayla (the price of liberty is eternal vigilance -- and eternal
  frustration [yes, I signed the loyalty oath: I needed the job.])
  I was required to have an IVP, too, as a condition of employment,
  after blood was found in my urine.  Nobody cared that I was
  menstruating when I gave the sample, and that as an allergy
  sufferer I was liable to fatal consequences from the imaging
  media.  I needed the job *a lot*, so I had the IVP, with an
  allergist on call in case I went into anaphalactic shock.  This
  in 1960: no drug testing involved, just a "routine physical" for a
  job as teacher in the NY City school system.  Repeat the urine
  test?  Oh, no, we wouldn't want to miss a possibly important
  diagnosis, would we, bayla?
 
  THIS ANECDOTE IS NOT MEANT TO SOLICIT SYMPATHY, BUT TO OFFER
  A REAL-LIFE EXAMPLE OF THE ABUSE OF 'TRIVIAL'POWER.