To test whether the Atlas motor controller is good you need a multi meter and a properly working Atlas Battery.
Install the battery in the frame.
Loosen the left crank clamping bolts (picture shows right side - you are doing the left only) with a m5 hex tool.
Remove the left crank retaining bolt (the picture shows the rigth side - you are only doing the left) with a m5 hex tool.
Remove the left side motor cover with a T15 tool. There are 4 bolts.
Unplug the yellow power plug from the motor.
Use a multimeter to read the voltage from the power port on the motor
if you get full battery voltage and it drops slowly the controller is good
if you get lower voltage or the voltage drops quickly, then your motor controller is bad
This video shows the process. https://www.youtube.com/watch?v=Jd4CzdGA7p4