If you have only one computer, connect both radios to that computer’s USB ports. Then choose two different terminal windows, like Tera Term and HyperTerminal on Windows, or CoolTerm and ZTerm on Macintosh. Pick one radio’s port in one program and the other radio’s port in the other program. Pretend that your first terminal program is one computer, and that your second terminal program is another one. Keeping all of this straight might make your head hurt a bit, but it’s a valid test when you can’t find a real second computer.