There are a lot of people and businesses who do hardware tests but not all of them are reliable, generally I avoid unknown youtube channels or websites and stick to known good sources. I will list some sources I think are good here and hopefully others will too.
CPU and GPU: Techpowerup.com, GamersNexus (youtube channel), anandtech.com (mostly cpu)
Monitors: rtings.com, Hardwareunboxed (youtube channel, they also do cpu and gpu but I don't consider them as good as the others above), tftcentral.co.uk
Coolers: techpowerup, gamersnexus
SSD: techpowerup, tomshardware (tomshardware reviews a lot of things but the quality of the site has gone down a lot I only visit for SSD reviews anymore)
PSU: cybenetics.com, old techpowerup and tomshardware reviews done by Aris Mpitziopoulos (not sure if he still does them because he runs cybenetics now)
