The answer to 'how to test surge protector' is to use a surge protector tester, which is a simple device that checks if the surge protector is functioning properly. This will let you know if the surge protector is still providing protection for your electronics and appliances.
To test your surge protector, first unplug it from the wall outlet. Then, plug the surge protector tester into the outlet where the surge protector was connected. The tester will have indicators that show if the surge protector is working correctly, or if it needs to be replaced. Follow the instructions on the tester carefully, and replace the surge protector if it fails the test.