trial by fire

noun trials by fire

1. countable, uncountable A test in which a person is exposed to flames in order to assess their truthfulness, commitment, courage etc. “[I]t seems to me Fra Francesco is the greater hero, for he offers to enter the fire for the truth, though he is sure the fire will burn him.” . . . “It is true, Messer Segretario,” said the shopkeeper, with subdued impatience. “But will you favour us by interpreting the Latin?” “Assuredly,” said Ti
2. countable, uncountable A situation in which a soldier or other combatant faces the discharge of opposing weapons, as a test of their fortitude. French troops, submitting to a trial by fire, drew toward the German forts, capturing and holding some machine-gun nests.
3. broadly, countable, idiomatic, uncountable Any ordeal which tests one's strength, endurance or resolve. But take it all in all, the overland trail was a trial by fire. One gets a notion of its deadliness from the fact that over five thousand people died of cholera alone.