Hey there, I believe the assessment for XC TM's involves the usual fairly generic railway testing, with 'Ticket Selling and Checking Tests', the RAAT (Rules Aptitude & Acquisition Test [?!] - or something like that) which would involve reading a passage of text and then answering multiple choice questions on certain aspects of it, and then a group 'activity' (test) of some kind designed to identify strengths and weaknesses in your communication skills. I'm told that this can take various forms, I know of one in which everyone in the assessment group has to read controversial statements and provoke group discussion, and I've heard of other types too, they rotate that test I believe so it's pot luck. Training is usually a couple of months or so in sunny Birmingham.
Hope that helps.