dry run, chiefly U.S. English (British English = dummy run)
idiom

- a practice of a particular activity or performance

(Cambridge Advanced Learner's Dictionary)

---
There are several theories regarding the origin of this expression. One of them involves dry stream or river beds commonly found in the U.S. that flood after a heavy rain. The idea here is that a practice or rehearsal is like a dry river bed before a storm.

Another explanation has to do with bootleggers, an American term for people who transported illegal liquor during Prohibition. This supposedly referred to creating the route before carrying out the transport. This explanation might also be associated with "dry counties," which are counties where the sale of alcohol is prohibited. This practice still exists today in some states in the U.S.

Last but not least, dry run may stem from the once common practice in the U.S. of fire departments exhibiting their skills at local festivals and carnivals. Sometimes instead of a "fire run," which is what most fire departments still call fire operations, they would do a "dry run," meaning they would perform an exercise or hold a competition with other fire departments without using water.

---
SYNONYMS
dummy run, practice run, rehearsal, test run, trial run


---
SMUGGLE OWAD into today's conversation

"We'll have a dry run of the presentation at 2:00 p.m. in the conference room."