They move quite slowly and appear to be strong enough. In practice no-one has raised an issue that the motors are missing steps, so there is no automated testing.
Tests for making the motion faster by gearing at 1:1 and 1:1.25 instead of the standard 2:1 are on GitLab, linked from Faster motion, different gearing - OpenFlexure Forum. That was done by tracking the image and checking that it moved as expected. There were no problems even with the required torque being more than twice as high as standard.