The most common and most likely answer to this crossword clue is the 3 plus 3 letter word DRY RUN
I've seen this crossword clue in Financial Times
D
R
Y
R
U
N
More clues leading to the result DRY RUN
- Forget lines, and flee rehearsal
- Not a Boat Race rehearsal, then
- For practice session, fail as well after switching halves
- Rehearsal for a TT race?
- Rehearsal: thirsty work
- Boring 13s of play a trial
- Fix odds in Derby fraud — no trial?
- TT race rehearsal
- Doctor has year with a French practice
- Test is dull — minimal scoring!
Buddy explains!

The straight part
We know that "Rehearsal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rehearsal = dry run.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.