circleci-test-configs

Overview

Configuration lives at .circleci/config.yml:

• Executors - where jobs run (Docker, machine, macOS).
• Jobs - individual units of work.
• Workflows - orchestrate jobs (sequential / parallel).
• Orbs - reusable, shareable config packages.

CircleCI's differentiator is test splitting - automatic parallelization based on per-test timing.

When to use

• Project is on CircleCI.
• Test suite is large enough for parallel splitting to matter (>5 min single-instance runtime).
• The team values orbs (per-tool reusable config).

Step 1 - Basic test config

# .circleci/config.yml
version: 2.1

jobs:
  test:
    docker:
      - image: cimg/node:22.0
    steps:
      - checkout
      - run: npm ci
      - run: npm test

workflows:
  test:
    jobs:
      - test

cimg/node:22.0 is CircleCI's pre-warmed Node image (faster startup than node:22).

Step 2 - Parallelism + test splitting

jobs:
  test:
    docker:
      - image: cimg/node:22.0
    parallelism: 4
    steps:
      - checkout
      - run: npm ci
      - run:
          name: Test (split by timing)
          command: |
            TESTS=$(circleci tests glob "tests/**/*.spec.ts")
            echo "$TESTS" | circleci tests split --split-by=timings | xargs npx jest
      - store_test_results:
          path: reports/junit

circleci tests split --split-by=timings reads prior run timings and distributes tests evenly across 4 parallel containers.

Step 3 - Multiple executors

executors:
  node-22:
    docker:
      - image: cimg/node:22.0
  node-20:
    docker:
      - image: cimg/node:20.0
  with-postgres:
    docker:
      - image: cimg/node:22.0
      - image: cimg/postgres:15.0
        environment:
          POSTGRES_PASSWORD: test

jobs:
  unit:
    executor: node-22
    steps:
      - checkout
      - run: npm test

  integration:
    executor: with-postgres
    environment:
      DATABASE_URL: postgres://postgres:test@localhost:5432/postgres
    steps:
      - checkout
      - run: npm run test:integration

  unit-on-node-20:
    executor: node-20
    steps:
      - checkout
      - run: npm test

The second container in the executor (postgres) is reachable as localhost from the primary container.

Step 4 - Workflow orchestration

workflows:
  test-and-deploy:
    jobs:
      - lint
      - unit:
          requires: [lint]
      - integration:
          requires: [unit]
      - e2e:
          requires: [integration]
      - deploy:
          requires: [e2e]
          filters:
            branches:
              only: main

requires: builds the DAG; filters: restricts when jobs run.

Step 5 - Orbs (reusable config)

version: 2.1

orbs:
  node: circleci/node@5.2.0
  codecov: codecov/codecov@4.2.0

jobs:
  test:
    docker:
      - image: cimg/node:22.0
    steps:
      - checkout
      - node/install-packages
      - run: npm test -- --coverage
      - codecov/upload:
          file: coverage/lcov.info

workflows:
  test:
    jobs: [test]

Orbs encapsulate common patterns (npm install, codecov upload, slack notify, etc.). Browse at circleci.com/developer/orbs.

Step 6 - Test results + artifacts

- run:
    name: Test
    command: npm test -- --reporters=default --reporters=jest-junit
    environment:
      JEST_JUNIT_OUTPUT_FILE: reports/junit/junit.xml

- store_test_results:
    path: reports/junit/

- store_artifacts:
    path: coverage/
    destination: coverage

store_test_results: parses JUnit XML and renders results in the CircleCI UI (Insights tab tracks flakes / slow tests over time).

store_artifacts: uploads files; viewable via the build's Artifacts tab.

Step 7 - Insights (CircleCI's analytics)

CircleCI Insights tracks per-test metrics:

• Flaky tests (passing then failing on retry).
• Slowest tests.
• Per-job duration trends.
• Pipeline duration.

Available via the project's Insights tab; no extra config needed (uses the data from store_test_results).

Step 8 - Contexts (shared secrets)

workflows:
  test:
    jobs:
      - integration:
          context: test-database-credentials

Contexts are project-organization-level credential stores - secrets shared across multiple projects without re-entering. Configured in Org Settings.

Step 9 - Conditional / parameterized

parameters:
  run-e2e:
    type: boolean
    default: false

jobs:
  e2e:
    when: << pipeline.parameters.run-e2e >>
    steps:
      - run: npx playwright test

# Trigger from API with:
# {"parameters": {"run-e2e": true}}

Useful for opt-in expensive tests (cross-browser, full regression).

Anti-patterns

Limitations

• CircleCI-specific. Migration to other CI requires rewrite.
• Test splitting needs prior run data. First run doesn't benefit; subsequent runs do.
• Cost model. Free tier limited; paid plans charge per minute / per resource class.
• Per-orb update cadence varies. Some orbs are stale.

References

• CircleCI docs at circleci.com/docs/.
• github-actions-test-jobs, gitlab-ci-test-jobs, jenkinsfile-test-stages - alternatives.
• ci-test-job-conventions - cross-CI conventions.