On most electric drives, the motor controller controls the ground for the drive motor/motors. They typically allow full positive voltage to the motor and varies the amount of ground thereby controlling drive speed. No way that I know that you can test the motor controller. You can do continuity test on the drive motor. Remove the cables from the four terminals, be sure and mark the cables so you know where they connect. Now, your terminal markings might be different, but you take a multitester set on ohms, or continuity beep if your tester has that,
connect test leads to F1 and F2, should have continuity
connect to A1 and A2, should have continuity
connect to A1 and F1, then A1 and F2, should have no continuity
connect A2 and F1, then A2 and F2, no continuity
connect lead to A1 and other lead to motor case (scratch through paint), should have no continuity
do the same on other terminals, A2, F1, F2 with one lead and other lead to motor case, no continuity