Help Capture return from AGI?

How can I capture the return value from my script?

I’m calling an AGI script and I’d like to know if it succeeds, or returns an error.

exten => START,1,AGI(tester.agi,${user})

I tried calling this with EXEC which supposedly has a return capability, but despite the script sitting in the agi directory, I keep getting an error that it can’t find the application.