Hello,
I guess the first thing you could do is power them up while connected to the console and see the routers and switches boot up.
If you do that successfully, then you may want to do a “show diagnostics post” and check the results from that output.
You can also do basic hardware test by connecting them up to a pc and see the interfaces come up okay.
All the above are just basic tests you could do, including leaving them running for sometime.
-HTH