trial by fire - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A test of one's abilities to perform well under pressure, as in Finishing this buge list of chores in time for the wedding is really a trial by fire. This expression alludes to the medieval practice of determining a person's guilt by having them undergo an ordeal, such as walking barefoot through a fire.