Making a servo tester using an Attiny85 micro chip, Attiny45 also works for this project. This diy servo tester is as good as ...

An Arduino is used to determine the servo’s current position versus the desired position, and it turns the motor accordingly with a BTS7960 motor driver.

Rather than write a bunch of stepper motor code himself, he installed and ran a four-axis fork of grbl on the Arduino, turning it into a stepper motor controller.