The best is probably to make a simulation software and then use a
null-modem cable and have your application talk to the simulator via a
loop-back serial link...But making the simulator could be some work
(if it's just a few commands to support it should be possible to make
within an hour, but that depends on your experience). The second best
is to have a VI that returns simulated data and then use that instead
of the serial VIs when testing. That does not test things as thorough
as the former method, but is probably quicker to implement.
