It sounds very much as though you are attempting both of these tests with no training; not uncommon, but not to be recommended from a safety perspective.
As
StrateandLevel said, i would seriously recommend the training. It's not like you're not gonna have any experience with the RT side of flying (you do your own in joining/departing and in circuit work anyway) but its consolidating those ideas that help
a lot. I did at course at Marshalls of Cambridge Aerodrome December 2001. It was a three - four day long course and at the end, on the very same day i took my written and passed (cant hint too much at whats in that, but others have answered a lot to that effect already). The consolidation course involved things like airspace types, restrictions for basic PPL liscence holders, emergency procedure radio calls [EFATO, forced landing and the like], and gave some practice on all aspects of a flight from A - B including QDF(QDR/QDM/QTR) if you get lost, reporting
or relaying a PANPAN or MAYDAY etc... Cant say all this was in the test, but its safe to know anyway.
I had a guy who flies 747 professionally with British Airways (Arwin Jones if you know him) take my RT practical. I remember him telling me I dont say Wilco enough (did that in December 2002). He made it really comfortable throughout, but I still slept well that night! The practical was also a complete flight and if Im correct in saying so, it includes everything tdw air-ground communications that anyone may encounter in their PFL or GFT, that means diversions, weather well below your liscence minima and danger to you or other pilots. There were many other little surprises in the test, including interaction with other people who were clearly not as good guiding me to my destination.
Basically you never know what a test has in store for you, but its a test. Just be sure to have the well rounded knowledge and it'll be like quizzing God on the laws of the universe.