For all but the simplest "plugins", I drop it into a vanilla LOCAL install of whatever version of ZC it is SUPPOSED to be compatible with.
If it falls over at this point, you know what you are dealing with....

If it does what is says on the tin, then drop it into a vanilla LOCAL version of the current ZC, same testing and fixing before letting it loose on your LOCAL development copy of your real site. I do all on php7 too, to flag up more things in advance.

So way before it gets anywhere near your real/production/non-broken/making-money so leave it alone as much as possible site you should have enough experience to trust or bin it.

Anyone who copies code from the "plugins" to their production site without testing it somewhere else first needs professional care.