[U-Boot-Users] Best way to see if a u-boot environment variable is defined with a script?

What would be the best way to see if a u-boot variable is defined with a script? In other words, I want to check to see if an env variable, say 'testvar' is defined from u-boot script (not from the interactive command line.) I tried to use itest and printenv, but doesn't seem to work.

Any suggestions?

Thank you.