The R/T test consists of two parts, a written paper (30 questions in 30 mins, multiple choice - study CAP413) and a practical test in which you sit in a room with a pair of phones etc. and 'fly' a route with the examiner acting as ATC. You have to deal with things like Mayday calls, controlled airspace penetration etc. It's not too hard but you can fail it if you just breeze in with no preparation at all. If you are training at an airfield with no ATC i.e. just air/ground or similar then I would recommend a bit of tuition first.
Cheers DB6