Set Up Test Parallelization

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Prerequisites

Before setting up Test Parallelization:

Set up Test Optimization.
For Ruby: use the datadog-ci gem version 1.31.0 or later.
For Python: use the ddtrace package version 4.11.0 or later and pytest.
For JavaScript: use the dd-trace package version 5.111.0 or later for v5 or v6.0.0 or later for v6, Node.js, and Jest.
Enable Test Impact Analysis for the test service when you want Test Parallelization to split only the tests affected by a code change.

Concepts

Runner: A program that runs tests. ddtest can run tests directly or write file lists for another runner.
CI node: One CI execution environment, such as a GitHub Actions job, CircleCI parallel container, Kubernetes pod, VM, or local machine.
Worker: A process started by ddtest to execute tests. One CI node can run one worker or multiple workers.
Plan: The generated .testoptimization/ directory. It contains the runnable test files, the selected parallelism, and per-node file lists used by ddtest run or another runner.
Selected parallelism: The CI node count or local worker count that ddtest chooses after estimating test file durations.

Install ddtest

Install the ddtest CLI in your CI job. Datadog publishes precompiled binaries in GitHub Releases.

- name: Download ddtest binary
  run: |
    mkdir -p bin
    gh release download --repo DataDog/ddtest --pattern "ddtest-linux-amd64" --dir bin
    mv bin/ddtest-linux-amd64 bin/ddtest
    chmod +x bin/ddtest
  env:
    GH_TOKEN: ${{ github.token }}

mkdir -p bin
curl -fsSL https://github.com/DataDog/ddtest/releases/latest/download/ddtest-linux-amd64 -o bin/ddtest
chmod +x bin/ddtest

Run on a single CI node

If you run your tests on a single CI node, run ddtest run:

bin/ddtest run --platform ruby --framework rspec

bin/ddtest run --platform python --framework pytest

bin/ddtest run --platform javascript --framework jest

By default, ddtest can start one worker for each physical CPU core available on the node.

Run across multiple CI nodes

For multiple CI nodes, run ddtest plan once, share the .testoptimization/ directory with every CI node, and pass each node its zero-indexed CI node number:

bin/ddtest plan \
  --platform ruby \
  --framework rspec \
  --min-parallelism 1 \
  --max-parallelism 8

bin/ddtest run \
  --platform ruby \
  --framework rspec \
  --ci-node <CI_NODE_INDEX>

bin/ddtest plan \
  --platform python \
  --framework pytest \
  --min-parallelism 1 \
  --max-parallelism 8

bin/ddtest run \
  --platform python \
  --framework pytest \
  --ci-node <CI_NODE_INDEX>

bin/ddtest plan \
  --platform javascript \
  --framework jest \
  --min-parallelism 1 \
  --max-parallelism 8

bin/ddtest run \
  --platform javascript \
  --framework jest \
  --ci-node <CI_NODE_INDEX>

In CI-node mode, ddtest uses one local worker by default. To start multiple workers in each CI node, set --ci-node-workers to a positive integer or ncpu.

For a list of available environment variables, defaults, and examples, see Configuration.

CI examples

Use the following examples as starting points for GitHub Actions and CircleCI.

Ruby

The plan job chooses the CI node count and emits a matrix. The test job downloads the .testoptimization/ artifact and runs only the files assigned to its matrix node.

name: CI with Test Parallelization

on: [push]

env:
  DD_TEST_OPTIMIZATION_RUNNER_PLATFORM: ruby
  DD_TEST_OPTIMIZATION_RUNNER_FRAMEWORK: rspec
  DD_TEST_OPTIMIZATION_RUNNER_MIN_PARALLELISM: 1
  DD_TEST_OPTIMIZATION_RUNNER_MAX_PARALLELISM: 8

jobs:
  dd_plan:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.dd_plan.outputs.matrix }}
    steps:
      - uses: actions/checkout@v4
      - name: Download ddtest binary
        run: |
          mkdir -p bin
          gh release download --repo DataDog/ddtest --pattern "ddtest-linux-amd64" --dir bin
          mv bin/ddtest-linux-amd64 bin/ddtest
          chmod +x bin/ddtest
        env:
          GH_TOKEN: ${{ github.token }}
      - name: Setup Ruby
        uses: ruby/setup-ruby@v1
        with:
          bundler-cache: true
      - name: Configure Datadog Test Optimization
        uses: datadog/test-visibility-github-action@v2
        with:
          languages: ruby
          api_key: ${{ secrets.DD_API_KEY }}
          site: datadoghq.com
      - id: dd_plan
        name: Plan test execution
        run: bin/ddtest plan
      - uses: actions/upload-artifact@v4
        with:
          name: dd-artifacts
          path: .testoptimization
          include-hidden-files: true

  dd_test:
    runs-on: ubuntu-latest
    needs: [dd_plan]
    strategy:
      fail-fast: false
      matrix: ${{ fromJson(needs.dd_plan.outputs.matrix) }}
    steps:
      - uses: actions/checkout@v4
      - name: Download ddtest binary
        run: |
          mkdir -p bin
          gh release download --repo DataDog/ddtest --pattern "ddtest-linux-amd64" --dir bin
          mv bin/ddtest-linux-amd64 bin/ddtest
          chmod +x bin/ddtest
        env:
          GH_TOKEN: ${{ github.token }}
      - uses: actions/download-artifact@v4
        with:
          name: dd-artifacts
          path: .testoptimization
      - name: Setup Ruby
        uses: ruby/setup-ruby@v1
        with:
          bundler-cache: true
      - name: Configure Datadog Test Optimization
        uses: datadog/test-visibility-github-action@v2
        with:
          languages: ruby
          api_key: ${{ secrets.DD_API_KEY }}
          site: datadoghq.com
      - name: Run tests
        run: bin/ddtest run --ci-node ${{ matrix.ci_node_index }}

The setup workflow runs ddtest plan, stores .testoptimization/, and continues into a test workflow with the selected CI node count.

In .circleci/config.yml:

version: "2.1"
setup: true

orbs:
  ruby: circleci/ruby@2
  test-optimization-circleci-orb: datadog/test-optimization-circleci-orb@1
  continuation: circleci/[email protected]

jobs:
  plan:
    docker:
      - image: cimg/ruby:3.4.1
    steps:
      - checkout
      - ruby/install-deps
      - test-optimization-circleci-orb/autoinstrument:
          languages: ruby
          site: datadoghq.com
      - run:
          name: Download ddtest
          command: |
            mkdir -p bin
            curl -fsSL https://github.com/DataDog/ddtest/releases/latest/download/ddtest-linux-amd64 -o bin/ddtest
            chmod +x bin/ddtest
      - run:
          name: Plan tests
          command: bin/ddtest plan --platform ruby --framework rspec
          environment:
            DD_TEST_OPTIMIZATION_RUNNER_MIN_PARALLELISM: 1
            DD_TEST_OPTIMIZATION_RUNNER_MAX_PARALLELISM: 8
      - save_cache:
          key: ddtest-plan-{{ .Revision }}
          paths:
            - .testoptimization
            - bin/ddtest
      - run:
          name: Continue with selected parallelism
          command: |
            desired=$(cat .testoptimization/runner/parallel-runners.txt 2>/dev/null || echo 1)
            printf '{"parallelism": %s}\n' "${desired}" > pipeline-parameters.json
      - continuation/continue:
          configuration_path: .circleci/test.yml
          parameters: pipeline-parameters.json

workflows:
  plan:
    jobs:
      - plan

In .circleci/test.yml:

version: "2.1"

parameters:
  parallelism:
    type: integer
    default: 1

orbs:
  ruby: circleci/ruby@2
  test-optimization-circleci-orb: datadog/test-optimization-circleci-orb@1

jobs:
  test:
    parallelism: << pipeline.parameters.parallelism >>
    docker:
      - image: cimg/ruby:3.4.1
    steps:
      - checkout
      - restore_cache:
          keys:
            - ddtest-plan-{{ .Revision }}
      - ruby/install-deps
      - test-optimization-circleci-orb/autoinstrument:
          languages: ruby
          site: datadoghq.com
      - run:
          name: Run tests
          command: |
            export DD_TEST_SESSION_NAME="ruby-tests-${CIRCLE_NODE_INDEX:-0}"
            bin/ddtest run --platform ruby --framework rspec --ci-node "${CIRCLE_NODE_INDEX:-0}"

workflows:
  test:
    jobs:
      - test

Python

The plan job chooses the CI node count and emits a matrix. The test job downloads the .testoptimization/ artifact and runs only the files assigned to its matrix node.

name: CI with Test Parallelization

on: [push]

env:
  DD_TEST_OPTIMIZATION_RUNNER_PLATFORM: python
  DD_TEST_OPTIMIZATION_RUNNER_FRAMEWORK: pytest
  DD_TEST_OPTIMIZATION_RUNNER_MIN_PARALLELISM: 1
  DD_TEST_OPTIMIZATION_RUNNER_MAX_PARALLELISM: 8

jobs:
  dd_plan:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.dd_plan.outputs.matrix }}
    steps:
      - uses: actions/checkout@v4
      - name: Download ddtest binary
        run: |
          mkdir -p bin
          gh release download --repo DataDog/ddtest --pattern "ddtest-linux-amd64" --dir bin
          mv bin/ddtest-linux-amd64 bin/ddtest
          chmod +x bin/ddtest
        env:
          GH_TOKEN: ${{ github.token }}
      - name: Setup Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.12"
          cache: pip
      - name: Install Python dependencies
        run: python -m pip install -r requirements.txt "ddtrace>=4.11.0" pytest
      - name: Configure Datadog Test Optimization
        uses: datadog/test-visibility-github-action@v2
        with:
          languages: python
          api_key: ${{ secrets.DD_API_KEY }}
          site: datadoghq.com
      - id: dd_plan
        name: Plan test execution
        run: bin/ddtest plan
      - uses: actions/upload-artifact@v4
        with:
          name: dd-artifacts
          path: .testoptimization
          include-hidden-files: true

  dd_test:
    runs-on: ubuntu-latest
    needs: [dd_plan]
    strategy:
      fail-fast: false
      matrix: ${{ fromJson(needs.dd_plan.outputs.matrix) }}
    steps:
      - uses: actions/checkout@v4
      - name: Download ddtest binary
        run: |
          mkdir -p bin
          gh release download --repo DataDog/ddtest --pattern "ddtest-linux-amd64" --dir bin
          mv bin/ddtest-linux-amd64 bin/ddtest
          chmod +x bin/ddtest
        env:
          GH_TOKEN: ${{ github.token }}
      - uses: actions/download-artifact@v4
        with:
          name: dd-artifacts
          path: .testoptimization
      - name: Setup Python
        uses: actions/setup-python@v5
        with:
          python-version: "3.12"
          cache: pip
      - name: Install Python dependencies
        run: python -m pip install -r requirements.txt "ddtrace>=4.11.0" pytest
      - name: Configure Datadog Test Optimization
        uses: datadog/test-visibility-github-action@v2
        with:
          languages: python
          api_key: ${{ secrets.DD_API_KEY }}
          site: datadoghq.com
      - name: Run tests
        run: bin/ddtest run --ci-node ${{ matrix.ci_node_index }}

The setup workflow runs ddtest plan, stores .testoptimization/, and continues into a test workflow with the selected CI node count.

In .circleci/config.yml:

version: "2.1"
setup: true

orbs:
  test-optimization-circleci-orb: datadog/test-optimization-circleci-orb@1
  continuation: circleci/[email protected]

jobs:
  plan:
    docker:
      - image: cimg/python:3.12
    steps:
      - checkout
      - run:
          name: Install Python dependencies
          command: python -m pip install -r requirements.txt "ddtrace>=4.11.0" pytest
      - test-optimization-circleci-orb/autoinstrument:
          languages: python
          site: datadoghq.com
      - run:
          name: Download ddtest
          command: |
            mkdir -p bin
            curl -fsSL https://github.com/DataDog/ddtest/releases/latest/download/ddtest-linux-amd64 -o bin/ddtest
            chmod +x bin/ddtest
      - run:
          name: Plan tests
          command: bin/ddtest plan --platform python --framework pytest
          environment:
            DD_TEST_OPTIMIZATION_RUNNER_MIN_PARALLELISM: 1
            DD_TEST_OPTIMIZATION_RUNNER_MAX_PARALLELISM: 8
      - save_cache:
          key: ddtest-plan-{{ .Revision }}
          paths:
            - .testoptimization
            - bin/ddtest
      - run:
          name: Continue with selected parallelism
          command: |
            desired=$(cat .testoptimization/runner/parallel-runners.txt 2>/dev/null || echo 1)
            printf '{"parallelism": %s}\n' "${desired}" > pipeline-parameters.json
      - continuation/continue:
          configuration_path: .circleci/test.yml
          parameters: pipeline-parameters.json

workflows:
  plan:
    jobs:
      - plan

In .circleci/test.yml:

version: "2.1"

parameters:
  parallelism:
    type: integer
    default: 1

orbs:
  test-optimization-circleci-orb: datadog/test-optimization-circleci-orb@1

jobs:
  test:
    parallelism: << pipeline.parameters.parallelism >>
    docker:
      - image: cimg/python:3.12
    steps:
      - checkout
      - restore_cache:
          keys:
            - ddtest-plan-{{ .Revision }}
      - run:
          name: Install Python dependencies
          command: python -m pip install -r requirements.txt "ddtrace>=4.11.0" pytest
      - test-optimization-circleci-orb/autoinstrument:
          languages: python
          site: datadoghq.com
      - run:
          name: Run tests
          command: |
            export DD_TEST_SESSION_NAME="python-tests-${CIRCLE_NODE_INDEX:-0}"
            bin/ddtest run --platform python --framework pytest --ci-node "${CIRCLE_NODE_INDEX:-0}"

workflows:
  test:
    jobs:
      - test

JavaScript

Use the same plan and test job structure as the Ruby and Python examples. Configure the runner and setup steps for Jest.

Set these environment variables at the workflow or job level:

env:
  DD_TEST_OPTIMIZATION_RUNNER_PLATFORM: javascript
  DD_TEST_OPTIMIZATION_RUNNER_FRAMEWORK: jest
  DD_TEST_OPTIMIZATION_RUNNER_MIN_PARALLELISM: 1
  DD_TEST_OPTIMIZATION_RUNNER_MAX_PARALLELISM: 8

Replace each language setup step with Node.js dependency installation:

- name: Setup Node.js
  uses: actions/setup-node@v4
  with:
    node-version: "22"
    cache: npm
- name: Install JavaScript dependencies
  run: npm ci

Configure Datadog Test Optimization for JavaScript:

- name: Configure Datadog Test Optimization
  uses: datadog/test-visibility-github-action@v2
  with:
    languages: js
    api_key: ${{ secrets.DD_API_KEY }}
    site: datadoghq.com

The ddtest plan and ddtest run --ci-node ${{ matrix.ci_node_index }} commands remain unchanged when the platform and framework are provided through the environment.

Use a Node.js image and set the runner environment in the plan job:

jobs:
  plan:
    docker:
      - image: cimg/node:22.14
    environment:
      DD_TEST_OPTIMIZATION_RUNNER_PLATFORM: javascript
      DD_TEST_OPTIMIZATION_RUNNER_FRAMEWORK: jest
      DD_TEST_OPTIMIZATION_RUNNER_MIN_PARALLELISM: 1
      DD_TEST_OPTIMIZATION_RUNNER_MAX_PARALLELISM: 8
    steps:
      - checkout
      - run:
          name: Install JavaScript dependencies
          command: npm ci
      - test-optimization-circleci-orb/autoinstrument:
          languages: js
          site: datadoghq.com

Keep the ddtest download, plan, cache, and continuation steps from the CircleCI workflow. In the test job, install dependencies, autoinstrument JavaScript, and pass the CircleCI node index to ddtest:

- run:
    name: Install JavaScript dependencies
    command: npm ci
- test-optimization-circleci-orb/autoinstrument:
    languages: js
    site: datadoghq.com
- run:
    name: Run tests
    command: |
      NODE_INDEX=${CIRCLE_NODE_INDEX:-0}
      bin/ddtest run --platform javascript --framework jest --ci-node "${NODE_INDEX}"

`ddtest` prepends `NODE_OPTIONS=-r dd-trace/ci/init` for Jest worker processes, so the project dependencies installed before `ddtest plan` must include `dd-trace`.

Use third-party test runners

Use ddtest plan files when you want ddtest to choose which files should run, but another runner should execute them.

To learn about the full contents of the plan directory, see Plan artifacts.

File	Use
`.testoptimization/runner/test-files.txt`	All runnable test files after Test Impact Analysis skips are applied.
`.testoptimization/runner/tests-split/runner-N`	Files assigned to CI node or worker `N`.

For example, use .testoptimization/runner/test-files.txt with Knapsack Pro:

KNAPSACK_PRO_TEST_FILE_LIST_SOURCE_FILE=.testoptimization/runner/test-files.txt bundle exec rake knapsack_pro:queue:rspec

For pytest, enable the ddtrace plugin with PYTEST_ADDOPTS and pass the file list to python -m pytest:

export PYTEST_ADDOPTS="${PYTEST_ADDOPTS:+$PYTEST_ADDOPTS }--ddtrace"
if [ -s .testoptimization/runner/test-files.txt ]; then
  xargs python -m pytest < .testoptimization/runner/test-files.txt
fi