Test parallelism conflict

May 15, 2026 · View on GitHub

Playbook ID: parallelism-conflict Category: test Severity: medium Tags: test, parallel, concurrency, port, database

What this failure means

Parallel test execution caused a resource conflict: two tests tried to bind the same port, access the same fixture, or write to the same temporary file simultaneously.

Common log signals

resource is busy
test is not parallelizable
concurrently
race detected
too many connections
database locked
concurrent =
re:concurrent access

Diagnosis

Parallel test execution caused a resource conflict: two tests tried to bind the same port, access the same fixture, or write to the same temporary file simultaneously.

Fix steps

  1. Reduce test parallelism with -parallel 1 to confirm the conflict is parallelism-related.
  2. Allocate a unique port, database, or temp directory per test rather than sharing a fixed resource.
  3. Use test-specific prefixes or random ports in each test's setup.
  4. If the suite must share a resource, serialize only the affected tests instead of disabling parallelism globally.

Validation

  • Re-run the failing workflow step.
  • Confirm the original failure signature for Test parallelism conflict is gone.

Likely files to inspect

  • docker-compose.yml
  • .github/workflows/*.yml
  • testdata/
  • internal/

Run Faultline

faultline analyze build.log
faultline explain parallelism-conflict
faultline workflow build.log --json --mode agent

Search phrases this page answers

  • Test parallelism conflict
  • Test: test parallelism conflict
  • re:running.*tests concurrently
  • faultline explain parallelism-conflict

Generated from playbooks/bundled/log/test/parallelism-conflict.yaml. Do not edit directly — run make docs-generate.