Watch your blood pressure and heart rate. Also, lots of test converting to DHT can cause problems with the prostate enlarging, which pushes it against your urinal tract (uhhh) and makes it tough to pee, and can ultimately lead to big problems.
What exactly do you mean high doses of test though? Ramp up your useage based on your weight and experience, if you think that going from 500mg a week to 1.5g a week is going to be good for you, you are wrong. There is only so much weight you can put on so fast, and the faster you put it on, the harder on your heart (since you are asking about side effects). It is a fact proven by many users, that making large jumps in doses is nothing but stupid, no more gains than before and only more sides.
Also, you can expect to sweat like a pig on test, once things start going for you. Some of this may just be the fast weight gain, I'm not really sure.
Deca, I've decided is something I wont touch.
Hope this is a helpfull start for you, good luck.