It would be more indicative of a tip off if they only tested the one. When I've been tested it's been along with everyone else within cooee with an ASIC.

As a flight crew member, I assume it's a fireable offense to know of a drunk crew member and not report it?

The answer is usually "C" if the test is multi choice.

...............

Knowing someone is under the weather, and being also aware of the law, it would be an interesting case to test out, but it would be common law not aviation law, unless the argument can be made that not terminating a flight with a known unfit crew member is a reckless act.

"Fire-able Offense"? Do you mean termination from position? Each country and airline probably have their own legislation regarding "failure to report". This is why we have barristers/lawyers and trade unions.

Have you spent much time in Singapore?