How would one go about connecting two processes which expect
to communicate over a serial line?

I'm running Linux. I have a protocol stack, the lowest layer
of which opens a serial port in non-canonical mode.

I would like to be able to start two instances of a test
application which uses the protocol stack and have them
communicate with each other on a single machine without
having to externally short two serial ports together.

I thought of pipes but:
a. writing to a pipe blocks; writing to a tty
doesn't;
b. pipes are unidirectional (or are they?); tty's are
bidirectional;

There must be an idiom for that.

--
JR