Continuous Integration

The short version

Continuous integration (CI) means every push automatically runs your tests, typecheck, and a build on a clean machine. I do not have to remember to do it. A machine that does not have my leftover local junk does the check.

Why it matters

CI catches breaks before merge, so I can trust main. "It works on my laptop" is not the same as a fresh checkout. If the check is green, the branch is safe to merge.

How it works

1. You push a branch.
2. A workflow starts on a clean machine.
3. You get a green check or a red check.
4. You merge only when it is green. Branch protection (required checks) blocks the merge until then.

Key concepts

• Commit: a save point with a message about what changed.
• Branch: a copy of the work so main stays clean.
• Pull request: the review, discussion, and checks wrapper before merge.
• Diff: what changed, line by line.
• Checks: the automated jobs (tests, typecheck, build).
• Caching and speed: reuse install folders so CI stays fast.
• Preview deploys: a live URL per branch, for example on Vercel, so you can click through the change.
• CI vs CD: CI proves the change is good. CD (continuous delivery or deployment) ships it.

Tips for AI-assisted development

• Write the spec first. I tell the agent what done looks like before it writes code.
• Let the agent open a PR. I review it on GitHub, not in chat.
• Read the diff. That is the real change, line by line.
• Don't trust an agent's reported test results. I let CI prove it on a clean machine.
• Keep PRs small. Small diffs are easier to read and cheaper to revert.
• Wait for checks before merging. Green means merge. Red means fix.
• Keep CI fast. I aim for under 2 minutes so I actually wait for it.
• Use the preview URL. I eyeball the change on a live page before I merge.

A tiny GitHub Actions workflow

Drop this in .github/workflows/ci.yml. Every push and pull request runs tests, typecheck, and a build.

name: CI
on:
  push:
  pull_request:
jobs:
  check:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
      - run: npm ci
      - run: npm test
      - run: npx tsc --noEmit
      - run: npm run build