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expect_fail

The expect_fail keyword marks a test as expected to fail. The test runner treats such a test as passing when it fails, and as failing when it unexpectedly passes, which guards against regressions that accidentally fix a known issue.

Syntax & Example​

test "not yet implemented" expect_fail {
    let result = feature();
    assert result == 42;
}

Use Cases​

  • Tracking known bugs and unimplemented features as explicit expectations.
  • Detecting when a previously-failing case starts passing.
  • Documenting intended behavior that is not yet supported.

See also: test, ignore.