I think the more important question you should be asking is, what is the school's procedure if a student fails a test.
Any (legitimate/reputable) training organisation which is providing a professional aviation course shouldn't just kick you out if you fail a test.
Generally, if you struggle with part of the TRAINING (for the Instrument Rating in your case), there should be some remedial (ground school and flying) to bring you up to speed before proceeding.
If you fail on a TEST, the same should apply...some additional ground training to address the deficiencies, one or more remedial flights (also to address the skills/proficiencies you failed on in the first test) and then a retest.
So, first thing...study your butt off and pass it on the first go. If you don't do so well, the school (if it is reputable) should provide you with necessary remedial and additional training to get you across the line. If the military is putting you through this course, they should be very unhappy with a training provider that threatens you with getting "kicked out" at the first sign of trouble.
Best of luck.