Although many schematic diagrams show pronounced teeth on the stator and/or rotor, this doesn’t have to be the case, as evidenced by e.g. this teardown of a 28BYJ-48 stepper motor by Cookie ...

How does a stepper motor turn into an encoder? Well, that’s the MacGyver part. We are not big fans of the physical circuit diagrams ... Of course, an Arduino reads the pulses.