Jest - Deployment and CI/CD

Quiz

In this chapter, we'll show you how to add Jest tests to your Continuous Integration(CI) and Continuous Deployment(CD) pipelines. This helps run tests automatically in different environments, so you can release your code faster and more reliably. The topics we'll cover are:

Jest - Continuous Integration
Jest - GitHub Actions
Jest - Deployment Strategies

Jest - Continuous Integration

Continuous Integration(CI) is when developers regularly commit code to a shared repository. The goal is to catch errors early by running tests whenever code is added to the main codebase. By integrating Jest with your CI pipeline, you can automatically run tests to verify your code works as expected after every change. Below are the steps to integrate Jest with CI.

Setting Up Jest for CI

To integrate Jest into your CI pipeline, you first need to ensure that your project is properly configured for Jest. Make sure that:

Jest is installed as a dev dependency: Run the following command to install Jest:

npm install --save-dev jest

Your test scripts are defined in package.json: In your package.json, add a test script to run Jest:

"scripts": {
    "test": "jest"
}

Running Jest in CI

Continuous Integration(CI) systems like Jenkins, Travis CI, GitHub Actions, and GitLab CI automatically detect your test scripts and run them when new commits are pushed to the repository.

To run Jest in a CI server, you will typically use this command to execute tests and generate a test report:

npm run test -- --ci --coverage

Configuring CI for Jest

Most CI platforms support easy integration with Jest. Here's an example configuration for a platform like Travis CI.

Create a .travis.yml file to define the build process:

language: node_js
node_js:
  - "14"  # Use Node.js version 14
install:
  - npm install  # Install dependencies
script:
  - npm run test  # Run Jest tests

In this example, Jest will automatically run whenever you push code to your Git repository.

Optimizing Jest for CI

To make Jest run faster and more efficiently in your CI environment, you can apply the following optimizations:

Parallelism: Jest runs tests in parallel by default, which speeds up the test process. You can control the number of worker threads Jest uses by setting the maxWorkers option.

"jest": {
    "maxWorkers": "50%"  # Limit to 50% of available CPUs
}

Disable Watch Mode: Since CI environments don't need to watch files for changes, make sure Jest's watch mode is disabled by default. The --ci flag automatically disables watch mode.

npm run test -- --ci  // Automatically disables watch mode

Test Coverage Reporting: Enable code coverage reports to track how well your tests cover your codebase. Jest can generate reports in different formats like lcov, json, or text.

npm run test -- --coverage  // Generate coverage report

By applying these optimizations, your Jest tests will run faster and more reliably in the CI pipeline.

Jest - GitHub Actions

GitHub Actions is a Continuous Integration and Continuous Deployment(CI/CD) service that allows you to automate tasks like testing, building, and deploying your code directly within GitHub. You can integrate Jest to automatically run tests whenever you push code to your repository.

Steps to Integrate Jest with GitHub Actions

Create a GitHub Actions Workflow File: In your GitHub repository, create a directory called .github/workflows if it doesn't already exist. Inside this directory, create a file for your workflow (e.g., jest-tests.yml).
Define the Workflow: In the workflow file, define the steps to set up your environment, install dependencies, and run Jest tests. Here's an example workflow for running Jest tests on GitHub Actions:

name: Run Jest Tests

on:
  push:
    branches:
      - main  # Run on push to the 'main' branch
  pull_request:
    branches:
      - main  # Run on pull requests targeting 'main' branch

jobs:
  test:
    runs-on: ubuntu-latest  # Run on the latest Ubuntu runner

    steps:
      - name: Checkout code
        uses: actions/checkout@v2  # Get the latest code from the repository

      - name: Set up Node.js
        uses: actions/setup-node@v2
        with:
          node-version: '14'  # Use Node.js version 14

      - name: Install dependencies
        run: npm install  # Install project dependencies

      - name: Run Jest tests
        run: npm run test -- --ci --coverage  # Run tests with coverage reporting

Run the Workflow: After setting up the workflow file, push it to your GitHub repository. GitHub Actions will automatically detect the file and start running the tests whenever a change is pushed or pull requests are made to the repository.

Monitor the Test Results: After the tests are run, you can view the results directly in GitHub Actions. Go to the "Actions" tab in your GitHub repository to see the status of the tests for each commit or pull request.

Jest - Deployment Strategies

After confirming your code works with Jest test, the next step is deployment. This section shows how to add Jest tests to your deployment pipeline to ensure tests run before the code is deployed to production.

Types of Deployment Strategies

Below are the common deployment strategies you can use to release your application:

Pre-deployment Testing: Before deploying your application, it's important to run Jest tests to ensure everything is working as expected. This step is important in any deployment strategy to catch bugs early and avoid problems in production.
Automated Deployment (CI/CD): In CI/CD (Continuous Integration/Continuous Deployment), your testing and deployment process is automated. After Jest tests pass successfully, your new code is automatically deployed. This method speeds up the release process while ensuring the code is stable.
Manual Deployment (with Testing): Manual deployment allows you to control when and how the new code goes live. However, before deploying the code, you still need to run Jest tests to make sure everything is stable and bug-free.
A/B Testing Deployment: A/B testing involves releasing two versions of your app (Version A and Version B) to different user groups to compare performance. Jest tests are run on both versions to ensure they work properly before deciding which one to keep.
Recreate Deployment: Recreate deployment means replacing the current version of your app with a new version. Before switching, you run Jest tests on the new version to confirm it works properly.
Canary Releases: Canary releases deploy a new version of your app to a small group of users first. Jest tests are run on the new version to catch any bugs before releasing it to a larger audience. If it passes the tests, the version is rolled out to more users.
Shadow Deployment (Dark Launching): Shadow deployment (also known as dark launching) is when you release a new version of your app without making it visible to users. Jest tests are run in the background to make sure the new version works correctly before you make it live.
Blue-Green Deployment: In Blue-Green deployment, you have two identical environments: one for the current version (Blue) and one for the new version (Green). Jest tests are run on the Green environment before switching users to it, ensuring no downtime or issues in production.
Continuous Deployment (CD): With continuous deployment, new code is automatically deployed every time it passes Jest tests. Jest tests are a key part of the pipeline, so only tested, stable code is released. This method helps teams release features faster.

How to Choose the Right Deployment Strategy in Jest?

Choosing the right deployment strategy depends on your project's needs. Consider these factors:

Project Size and Complexity: For smaller projects with fewer dependencies, simpler strategies like blue-green deployment or rolling deployment might work well. Larger projects with more complex requirements could benefit from advanced strategies like canary deployment or A/B testing.
Availability and Scalability Needs: If your application needs to handle high traffic or you need the ability to update quickly, strategies that support rolling updates will be helpful.
Available Resources: If your team is small or lacks experience with advanced strategies, choose simpler deployment methods that are easier to manage and maintain.
Impact on Users: Make sure to choose a deployment strategy that minimizes downtime and ensures a smooth experience for your users during updates.

Best Practices for Deployment with Jest

To achieve smooth deployment, follow these best practices for integrating Jest tests:

Run Jest Tests Before Deployment: Always include Jest tests in your deployment process, whether automatic or manual, to catch issues early.
Monitor After Deployment: Keep an eye on your app in production, even after Jest tests pass, to spot any unexpected problems.
Optimize Jest for Faster Execution: In CI/CD setups, make sure Jest tests run quickly to avoid delays in the deployment process.
Configure Jest for Your Deployment Strategy: Adjust Jest settings to fit your deployment method, like Canary or A/B testing, for better results.

Print Page