src/test/ui/lint/force-warn/force-allowed-deny-by-default-lint.rs

// compile-flags: --force-warns const_err -Zunstable-options
// check-pass

#![allow(const_err)]
const C: i32 = 1 / 0;
//~^ WARN any use of this value will cause an error
//~| WARN this was previously accepted by the compiler

fn main() {}