So now we have several nonrandomly selected data points on either side - which proves only that some employers test and some don't.
Most every industrial employer is the same.
Have any more evidence for that claim than "every company you’ve ever worked for"?
“Firms implementing drug testing programs also can be
distinguished by type of industry. The 1989 Conference
Board survey showed that three-fourths of the companies
with drug testing programs were manufacturers or gas and
electric utilities, while nearly half of the companies that reported
not having a drug testing program were in banking,
insurance, and other financial service industries.”
http://www.bls.gov/opub/mlr/1996/11/art4full.pdf