A tryout, practice version, or rehearsal of something planned: One more dry run, then tomorrow we do it(1940s+)
: so the medical staff could ''dry run'' their equipment
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with dryrun
A trial exercise or rehearsal, as in Regard this as a dry run for tonight's ceremony. This term, using dry in the sense of “unproductive,” was at first employed mainly in the military for simulated bombings in which no bombs were dropped.
[ c. 1940