Ask HN: How to properly unit-test for embedded system application?

I worked in a startup that builds embedded system, but they didn't have proper way of doing unit testing in my opinion. What we did was writing some testing code, and check the output on a USB serial terminal. We didn't have any automated test. For sensors, we check if outputs are what we expect. For motors, we do position control, so we plot the trajectories to see if the controller is tracking well. We had FSM in the system, and we manually input to make state transitions. Is this the right approach for doing tests or unit-tests on embedded systems? What are some resources to learn the proper way of doing tests?