dune "build @runtest ... FAILED" in CI

dune runs your tests through the @runtest alias. A failure means an expect/cram test produced output that differs from the recorded expectation, or a test raised an uncaught exception and exited non-zero.

What this error means

dune build @runtest or dune runtest fails, printing a diff between expected and actual output, or a "Fatal error: exception ..." from a failing test.

File "test/test_calc.ml", line 1, characters 0-0:
Fatal error: exception Failure("expected 5, got 6")
FAILED test/test_calc.exe (exit 2)

Common causes

A real test assertion failed

The code under test produced a wrong result, so an assertion raised or an expect diff appeared.

A stale recorded expectation

The expected output in a cram/expect test drifted from intended behavior and needs promoting.

How to fix it

Read the diff or exception and fix the code

1. Read the printed diff or "Fatal error: exception ..." line.
2. Fix the code so the actual output matches the expectation.
3. Re-run dune runtest to confirm it passes.

dune runtest --force

Promote intended output changes

When the new output is correct, promote it so the recorded expectation matches, then commit the change.

dune runtest
dune promote

How to prevent it

• Run dune runtest locally before pushing.
• Promote expect/cram changes deliberately, reviewing the diff.
• Keep tests deterministic so CI matches local output.

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