Some tests, like HUBS and CELS GLMs, only allow limited attempts. That's from Blackboard, not from CELS. A bit like when they said in introductory lectures that "some of you will not get into med" - it doesn't necessarily mean you.
Unless you see a bold "You are allowed 3 attempts at this test", it's generally unlimited.
PS: I thought Phil Bishop would've said in the intro lecture "you can go sit it, get 9/10, then go out, have a couple of drinks, come back, sit it again, and get 2/10, but your highest one will count" like he did last year.