A couple of things I'd add to what has been said above.
Remember, you are trying to sell to the examiner the concept that you are a competent safe pilot. No examiner expects perfection - although they may discuss some of the less than perfect points with you. Mine demonstrated several things during the test. I still passed (and that was after me demonstrating an accidental spiral dive from a steep turn!)
A great deal of this is about your professional attitude. Try to relax and remember that, even during the test, you should be enjoying flying. The most likely thing, if you stuff something up, is that you will be deferred. That is not the end of the world and does not equate to that other great dread in life - failing the driving test!
If you can, opt to do the nav first. That gets you used to flying the plane in the conditions on the day.
Finally, I haven't read the rules about provision of aircraft for the test - which probably require a working radio - but since when has a faulty PTT button rendered an aircraft unairworthy? Seems to me like the examiner lacked a certain amount of common sense and discretion; if you had passed the radio test previously, he could have opted to do all the radio work himself.
HH