in my experience:
it is considered rude to ask sensei about testing directly ie "your" testing, general questions about testing are ok.
testing is somewhat of a formality ie sensei feels that you are at that level thus it is recognition of your growth.
talk of failing a test is ridiculous this indicates that sensei has no grasp of your abilities.
in some schools testing is merely economic ie lots of kyu ranks, stripes on belt, more tests means more testing fees...
there is also no standard or standard curriculum from school to school ie in some you do the time you get the belt, in others you have to demonstrate barely any thing to attain rank , in others it is incredible the amount of stuff you must know and demonstrate...
in conclusion dont worry about it just practice colored belts are for sissys
if you practice you will get better thats what matters