[bitbiter]

Electronic gambling machines are highly regulated because they deal with real money and random number generation. There are a lot of safeguards in that industry across various jurisdictions that seem like they should apply to electronic voting machines too.

Independent testing laboratories exist that do specialize in the specific skills you're talking about. Pretty much all of the software involved is certified and saved, source is saved, compiled binaries are saved, hashes are logged of the compiled binaries. Binaries run from EPROMS or write-protected partitions making it very difficult to change them once installed. Cabinets have tamper-apparent sealing.

The machines are designed so that an auditor can inspect a machine on a casino floor in under 5 minutes, verifying that the software that's installed is the one that's supposed to be and that the physical seals haven't been broken.

I'd imagine there are a lot of similar processes for ATMs.