Final answer:
Pressing the ENG 1 (2) TEST pushbutton on a fire panel successfully tests the corresponding engine when the fire indicator light illuminates.
Step-by-step explanation:
When the ENG 1 (2) TEST pushbutton is pressed on a fire panel, a successful test is indicated by the activation of the corresponding fire indicator light for the engine being tested.
For example, if the ENG 1 TEST pushbutton is pressed and the ENG 1 fire indicator light illuminates, it indicates that the test on the first engine is successful.
Similarly, if the ENG 2 TEST pushbutton is pressed and the ENG 2 fire indicator light illuminates, it indicates a successful test on the second engine.