Acid test:

Acid test: 1. A rigorous test of authenticity, from the testing of gold with nitric acid. 2. Nasty moment when it becomes apparent that it’s simply not going to work; time to retire hastily to the pub to lick wounds and have a re-think; conclusive proof that it’s a shambles; irrefutable evidence of incompetence. (see Blue touch paper, light the; Proof of concept)

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