How can I test that my stepper motors for functionality and compliance?
For the AliExpress part, open a dispute and attach pictures to the dispute and ask for a partial, reasonable discount. It always worked for me.
As for how to test the motors themselves, it depends on what other hardware you have.
For example, you could wire the motors to your printer board, and try to issue a G6 command to that motor.
If you find issues while testing the motors, that could be evidence for an even bigger discount, or even full refund if the motor doesn't work.