The AAMC Mini Exams are composed of questions from AAMC (I recommend gaining access to all of the AAMC’s practice problems by purchasing the Online Only Bundle and the AAMC Flashcard Pack). There are 12 AAMC Mini Exams total, and you will complete two during MCAT Bootcamp one at the end of each of the 10 Content Modules (during lesson 15).
For instance, after completing your first Content Module, you’ll complete your first AAMC Mini Exam by completing problems from four different AAMC question packs as outlined here (lesson 15 of each Content Module contains an outline for all 12 Mini Exams):
AAMC Mini-exam 1
For Chemistry/Physics Section, take 30 minutes to complete problems 1 through 19 from the Official MCAT Chemistry Question Pack (5, 6, 7, 8, 9, 11, 13).
For Critical Analysis and Reasoning Section, take 33 minutes to complete problems 1 through 21 from the Official MCAT Critical Analysis and Reasoning Skills Question Pack, Volume 1.
For Biochemistry/Biology Section, take 30 minutes to complete problems 1 through 20 from the Official MCAT Biology Question Pack, Volume 1.
For Behavioral Sciences Section, take 20 minutes to complete problems 1 through 12 from the Psychological, Social, and Biological Foundations of Behavior Section in the AAMC MCAT Section Bank.
By completing all four sections of the Mini Exam, at the end of each content module, you will gain a fresh perspective on your overall MCAT score, and you will begin to see how you are progressing within each individual subsection.  I strongly encourage the completion of an AAMC Mini Exam at the end of every Content Module.