a dummy run
A practice session or test designed to identify and correct possible problems. Primarily heard in UK, Australia. Let's do a couple dummy runs of your speech so you feel totally comfortable with it for tomorrow's ceremony. The theater group did a dummy run of the play to iron out any technical problems before opening night.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a dummy runBRITISH
A dummy run is an occasion before an important event when you practise doing something, in order to make sure that it will be successful when you do it properly. Before we started, we did a dummy run, checking out all the streets and offices we would use, and planning our escape route. If it is not possible to do a dummy run in the hire car, calculate how long the journey to the church will take on the day.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012