The reason why you can only shoot yourself in test mode is becoz, in normal battle mode, when you fire your IR(main gun) the MFU "turns off" your receiver at the same time so you do not shoot yourself. That is also the reason why sometimes when 2 tanks fire at each other at the same time, neither gets hit, though sometimes 1 tank does get hit due to the slight difference in the timing of the 2 shots.