What testing tools have you worked with? How were the tests integrated into CI?

In frontend development, Jest is often used for unit testing React components, as well as Cypress for e2e tests. Tests are usually run through npm scripts, for example, npm test for Jest and npm run cypress:run for Cypress.

Integration into CI is done through configuration in systems like GitLab CI, Jenkins, or GitHub Actions. A step is added in the pipeline to run tests, and if they fail, the build is marked as unsuccessful. Example for GitHub Actions:

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Install dependencies
        run: npm install
      - name: Run tests
        run: npm test

Thus, tests are automatically checked with each commit or pull request, ensuring code quality.