Spurious warning "Arguments in ... must be used" if an error is not triggered and fixed = TRUE

[mcol]

See this testcase: as the function is not producing an error, I would expect one error to be reported:

test_that("showing problem", {
  local_edition(3)
  expect_error(identity(1),
               "Error message", fixed = TRUE)
})

Instead, besides an error I also get a warning and backtrace just because I am using fixed = TRUE:

══ Testing test_test.R ══════════════════════════════════════════════════
[ FAIL 1 | WARN 1 | SKIP 0 | PASS 0 ]

── Failure (test_test.R:3:3): showing problem ──────────────────────────────────
`identity(1)` did not throw the expected error.

── Warning (test_test.R:3:3): showing problem ──────────────────────────────────
Arguments in `...` must be used.
x Problematic argument:
* fixed = TRUE
i Did you misspell an argument name?
Backtrace:
     ▆
  1. ├─testthat::expect_error(identity(1), "Error message", fixed = TRUE) at test_test.R:3:3
  2. │ └─testthat:::expect_condition_matching(...)
  3. │   └─rlang (local) `<fn>`()
  4. │     └─rlang:::check_dots(env, error, action, call)
  5. │       └─rlang:::action_dots(...)
  6. │         ├─rlang (local) try_dots(...)
  7. │         │ └─rlang::try_fetch(expr, error = error)
  8. │         │   ├─base::tryCatch(...)
  9. │         │   │ └─base (local) tryCatchList(expr, classes, parentenv, handlers)
 10. │         │   │   └─base (local) tryCatchOne(expr, names, parentenv, handlers[[1L]])
 11. │         │   │     └─base (local) doTryCatch(return(expr), name, parentenv, handler)
 12. │         │   └─base::withCallingHandlers(...)
 13. │         └─rlang (local) action(...)
 14. │           └─rlang:::signal_abort(cnd, .file)
 15. │             └─base::signalCondition(cnd)
 16. └─rlang (local) `<fn>`(`<rlb_rr__>`)
 17.   └─handlers[[1L]](cnd)
[ FAIL 1 | WARN 1 | SKIP 0 | PASS 0 ]

[hadley]

Duplicate of #1932 (which should be fixed shortly)