linux software to emulate a serial port device

Hello,
my client want me to write a java app that communicates with a VMC (vending machine controller) device.

the problem is that my client is in another country and i don't have the VMC so i can plug it to my machine serial port and communicate with it through java comm API.

are there some techniques to connect remotely to my client machine and try running my java program as it is run on remote client machine?
i mean is there a way to tell my machine that this remote VMC is virtually plugged in some port and try doing tests as if the VMC was actually conncted to my local machine?

thanks

i don't know what device i should plug into my computer to test with?
it shouldn't be a USB device but a serial port device. is there a software for linux that simulates a serial port device that we can communicate (send/receive commands and data) with without having a real physical device connected to machine?

thanks