CI Basics

1 The Hook — Why This Matters

A Dunedin software agency had a talented automation engineer who wrote 150 beautiful Playwright tests. They sat in a repo, untouched, for six months. Why? No one had wired them into the build pipeline. Developers continued merging code without running the suite. When the client finally demanded automated regression, thirty-seven tests failed immediately — not because the application was broken, but because the tests had drifted from six months of UI changes.

Tests in CI are the only tests that matter. Everything else is documentation that might be wrong.

2 The Rule — The One-Sentence Version

Manual test execution doesn't scale. If a developer has to remember to run tests, they won't. CI is your enforcement mechanism and your safety net.

3 The Analogy — Think Of It Like...

4 Watch Me Do It — Step by Step

Here is a complete GitHub Actions workflow that runs a Playwright test suite.

1. Create the workflow file

   # .github/workflows/test.yml
   name: Test Suite
   on:
     push:
       branches: [main]
     pull_request:
       branches: [main]
   
   jobs:
     unit-tests:
       runs-on: ubuntu-latest
       steps:
         - uses: actions/checkout@v4
         - uses: actions/setup-node@v4
           with:
             node-version: "20"
             cache: "npm"
         - run: npm ci
         - run: npm run test:unit
   
     e2e-tests:
       runs-on: ubuntu-latest
       needs: unit-tests
       steps:
         - uses: actions/checkout@v4
         - uses: actions/setup-node@v4
           with:
             node-version: "20"
             cache: "npm"
         - run: npm ci
         - run: npx playwright install --with-deps
         - run: npx playwright test
         - uses: actions/upload-artifact@v4
           if: failure()
           with:
             name: playwright-report
             path: playwright-report/

2. Understand the key concepts

   Concept	What it is
   Workflow	YAML file defining an automated process
   Job	A set of steps running on the same runner
   Step	An individual task (command or action)
   Action	Reusable unit (e.g., actions/checkout@v4)
   Runner	The VM/container executing jobs

3. Add triggers for your needs

   on:
     push:
       branches: [main, develop]
     pull_request:
       branches: [main]
     schedule:
       - cron: "0 2 * * *"  # nightly at 2am UTC

4. Cache dependencies

   - uses: actions/cache@v4
     with:
       path: ~/.npm
       key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

e2e-tests:
  runs-on: ubuntu-latest
  strategy:
    matrix:
      shard: [1, 2, 3, 4]
  steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-node@v4
    - run: npx playwright test --shard=${{ matrix.shard }}/4
    - uses: actions/upload-artifact@v4
      if: failure()
      with:
        name: playwright-report-shard-${{ matrix.shard }}
        path: playwright-report/

5 When to Use It / When NOT to Use It

6 Common Mistakes — Don't Do This

7 Now You Try — Interview Warm-Up

8 Self-Check — Can You Actually Do This?

Click each question to reveal the answer. If you got all three, you're ready to practice.

9 Interview Prep — Mid-Level Q&A

Interviewers ask about pipeline design, failure handling, and how you've troubleshot CI issues. Here are common scenarios.