Sergio Perez confirmed that he was subjected to a very "early morning" surprise urine test.
Daniel Ricciardo mentioned on twitter that he, "Got drug tested in the early hours this morning. All of a sudden pissing in your own home becomes difficult with someone staring over your shoulder."
Fernando Alonso's tweet read, "06:42h. Control antidoping."
All Formula One drivers are covered under WADA standards which includes testing at Grands Prix, but they can also be tested out of competition.