It's called fuzzing.

Fuzzing does not catch all bugs. And even if it, did your software can still misbehave when all logical bugs are eliminated. Say for example the program parses correctly but uses up a large amount of RAM on certain inputs, causing occasional crashes and restarts in production. Say for example your program behaves perfectly but there's actually an occasional bug in the date formatting in the logs themselves.

So yeah, you need monitoring and assertions. A decent coverage of unit tests is good, but I wouldn't bother trying to invest in some sort of advanced fuzzing or quickcheck system. In my experience the juice isn't worth the squeeze.