There is a package called `stress` that can be used to literally "stress" a system - depending on your system specs would determine how many cpu cores you would want to utilize in the test, I've never run it with more than my system had, (but now I'm curious). I don't think it's a default package however, so you might need to apt/yum/pacman/emerge as necessary.
running it looks something like this:
stress --cpu 4 --io 4 --vm 4 --vm-bytes 1024M --timeout 10s
you can find more info on it by checking info:
info stress
I usually run it in one terminal window then have another running my process monitor (top, htop, conky etc) to observe and tweak the parameters.
Hope this helps!