If some of these fail, then "ok" is a poor choice of name prefix.
Names based on what each is testing would be cumbrously long, so I can understand chosing to use a prefix.
Calling them test1, test2, test3 and so on would be clearer, I think; alternatively, have the ones that fail use "not" in place of "expression" so that ok1, etc. are suitable names.  Or they're all predicates, so p1, p2, p3 etc.