The ECU has many sensor inputs and actuator outputs.
The Actuators do something physical, they have movement, usually there are solenoids, relays or vacuum solenoid valves, or motors (cruise box), or even spark and the fuel pump motor are actuators.
G16 A or B engines.
The coils can be tested for Resistance, easy. here is one list. (the 89/90 ISC coil is 6 ohms and later years are 12 ohms. No mixing allowed.
If the coils are good we can apply 12vdc with a battery to its 2 pins, and see them work and furter test them.
The injectors are are solenoid fuel valves , in truth and are 12-17 ohms on MPI and 0.8 to 1.8 ohms on TBI G16a engines.
The VSV are 25-30 ohms (Vacuum solenoid valves)
The Fuel pump and ECU main relay are 122 to 149 ohms. the other relays are here.
If any coil reads infinity then that coil is open circuited and 100% dead.
The spark coil has 2 coils, primary and secondary. The primary 10 ohms secondary 20,000 ohms,as seen here
Acuators of all types have many failure modes. stuck open ,closed or dead, open coil , clogged with gunk. (or leaks fuel)
There are actuators that are motors, like the J18 engine EGR or ISC motor drive. These to can be tested. (the FSM is best source of facts on the J18/J20 and larger engines.)
All sensors are covered here and most actuators.
And Videos for these items are here.