That's crazy. Failing a drug test is probably not legal cause to evict you, and refusing to take the test almost certainly is not. Of course they can do a no-cause eviction if you don't have a lease.

Landlords can and do put all kinds of unenforceable clauses in leases, though. There's no incentive not to because some people will see that they've violated an unenforceable clause and simply move out assuming that it is legal.