This occasionally crops up. It's nothing like the trainee assessments and a failure won't affect your current employment at all. I think you do the SCAAT test which trainee candidates do, then a few other bits and bobs, reading a passage then remembering some key info. Just used internally to aid with selection. Seems a bit daft really, you'd think a proven safety record and interview would be enough for a decent recruiter to be going on with.