trial by fire

“[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 Tito. “It does but express the conclusions or doctrines which the Frate specially teaches, and which the trial by fire is to prove true or false.”

French troops, submitting to a trial by fire, drew toward the German forts, capturing and holding some machine-gun nests.

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.