Say you use PuTTY serial mode and a USB to RS232 cable. Can you send messages to yourself if you wire the TX of the cable back to its RX, not haphazardly, there's probably a bit more set up detail. I'm just wondering if it's possible to self-talk on the putty terminal using serial by routing wires back to yourself.
Yes that usually works. And you don't have to provide anything special. If you are paranoid you can place a series resistor there when doing the connection, but that is not necessary as the voltage levels on the pins are compatible.
It will look like a loopback, depending on the terminal settings you might see everything twice if the program is printing the typed stuff on its own already.
Yes, it will work. It is a very convenient test when solving communication issues with devices to pinpoint where the problem is.