An ice maker is a very simple device.
One part is the freezer. That system maintains the box at a very cold temperature, about 0°F. Measure the box temperature to ensure it is good.
The other part is the ice cube tray system. It has a cycle timer. The timer is a geared-down motor w/ contacts placed along the cycle.
The ice cube tray system has a snap action thermostat measuring the ice cube tray temperature. When the thermostat is "happy", below 32°F, it starts the cycle timer.
The cycle timer first runs the tray dump, then runs the water valve, then waits until the next time the thermostat is happy.
The suspect valve could be tested by application of power to verify opening and flow.
The thermostat can be verified w/ an ohm meter.
The cycle timer can be verified by closing the thermostat contact.
