Pseudo terminal for comms between two processes

I am writing an executable that uses a 3rd party C library (libmodbus if it matters) to communicate via serial device (in my case, /dev/ttyUSB0 or similar to talk RS-485 via an FTDI chipset based USB-to-RS485 adapter). This executable, based on CLI args, can initiate commands (in my case, act like a modbus client) then await a response (in my case, from an external modbus server), or listen for incoming commands (in my case, act like a modbus server) then generate a response. I would like to automate the testing of my executable, without a need for some external device. In other words, I'd like to launch two instances of my executable, where: - The first instance is put into modbus client mode and uses /dev/xxxx for comms - The second instance is put into modbus server mode and uses /dev/yyyy for comms - Set up /dev/xxxx and /dev/yyyy to both act as serial devices that are are essentially the two ends of the same wire. From what I read on pty manpage , I believe /dev/xxxx and /dev/yyyy are the two ends of a pseudo-terminal. Which brings me to my questions: 1. The man page refers to BSD-style pseudoterminals which seem more appropriate to what I am trying to do. - Is my understanding of BSD-style pseudoterminals correct? - If so, is it possible to create BSD-style pseudoterminals on non-BSD linux distributions? In pacticular, I am using debian 10, 11, 12 (and debian based, like Ubuntu 20.04, 22.04) 1. The man page also refers to UNIX 98 pseudoterminals, which are implemented using posix_openpt(). However, even after the subsequent grantpt() and unlockpt(), I can only one one /dev/pts device for the client side of the pty, with the master side being only a file descriptor inside the executable. - Is my understanding (which is loosely based on code like this ) correct? - If so, what tricks may I use to convert the master side file descriptor to an proper /dev/xxxx which is the only API available to get a modbus context 1. Are there other "standard" linux tools for doing what I am attempting to do? It seems like tools like the ones mentioned here are expecting to connect an executable's STDIO to the pty.