Why I cannot emulate a serial device (arduino or somethin else) using socat?

I want to fake a device via a script and have the dart program to interface with it Therefore, in my linux machine, I've run the following command to emulate a serial port:

socat PTY,link=./arduino-sim,raw,echo=0 PTY,link=./virtual-tty,raw,echo=0

And I've made a session via screen that will emulate the virtual device:

screen