How do I test a Knock sensor on a 97 Toyota 4runner V6

I got a code for a knock sensor #2 after replacing it I drove the vehicle and this time I got code for knock sensor #1. I did replace it and them I got code for both sensors. So I thought I should replace the wire harness to the sensors and I did it. The problem persist and after following steps to troubleshooting I decided to replace the computer as the troubleshooting guide says. I did replace the computer but the problem still there. The only thing I have not done now is to test the sensors because I do not know how to.