How to tell what a command returns?

Hello all,

Novice at SoapUI coding, so apologies if this is a stupid question.  Haven't been able to find an answer in the Help, though.

Is there a way to tell exactly what a command is returning?  For example, if I create a custom property and then call it in a Request, it just gives me an error.  It would be very helpful if there were a tool I could use to tell exactly what the return of the command is instead.

Example command: ${=String.valueOf('2014-'&'(Math.Random() * (12 - 01) + 01)'&'-01')}

Thank you!