Required Checks

The Hook (The "Byte-Sized" Intro)

What if a PR with failing tests could never be merged? Required status checks make that a reality. The merge button stays grey until CI passes — lint, tests, build, security scan. No exceptions. No "I'll fix it later." The quality of main is mathematically guaranteed by automation.

📖 What are Required Checks?

Branch protection rules that mandate specific CI/CD checks must pass before a PR can be merged into a protected branch.

Conceptual Clarity

Common required checks:

Check	What It Validates	Speed
Lint	Code style compliance	Fast (< 30s)
Unit tests	Logic correctness	Medium (1-5 min)
Build	Code compiles/bundles	Medium (2-5 min)
Type check	TypeScript/type errors	Fast (< 1 min)
Security scan	Vulnerability detection	Medium (1-3 min)
Integration tests	Cross-service behavior	Slow (5-15 min)

"Strict" mode:

Setting	Effect
Strict OFF	Checks run on PR branch as-is
Strict ON	Branch must be up-to-date with base before merge

Strict mode prevents "green PR that breaks main" — where two PRs individually pass but conflict when both merge.

Real-Life Analogy

Required checks are like building inspections. You can build the house (write the code), but before anyone moves in (merge to main), the inspector (CI) must sign off. No shortcuts, no self-certification.

Visual Architecture

flowchart LR PR["📋 PR"] --> LINT["✅ Lint"] LINT --> TEST["✅ Tests"] TEST --> BUILD["✅ Build"] BUILD --> MERGE["🔀 Merge Allowed"] style MERGE fill:#1b2d1b,stroke:#53d8fb,color:#53d8fb

Why It Matters

Quality guarantee: Broken code never reaches main.
Confidence: Every merge is validated by automation.
Speed: Reviewers focus on logic, not style or test failures.
Accountability: Failures are visible and tracked.

Code

yaml

# ─── GitHub Actions workflow ───
# .github/workflows/ci.yml
name: CI
on:
  pull_request:
    branches: [main]

jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm ci
      - run: npm run lint

  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm ci
      - run: npm test

  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
      - run: npm ci
      - run: npm run build

bash

# ─── Set required checks via GitHub CLI ───
# In branch protection settings, add:
# Required status checks: "lint", "test", "build"
# Require branches to be up-to-date: ✅

Key Takeaways

Required checks block merging until CI passes — lint, tests, build.
Strict mode requires the branch to be up-to-date with main before merge.
Define checks in CI workflows; reference them in branch protection.
Fast checks (lint) and slow checks (integration) can run in parallel.

Interview Prep

Q: What are required status checks? A: Branch protection rules that require specific CI jobs (lint, tests, build) to pass before a PR can merge. The merge button is disabled until all required checks show a green status.
Q: What does "strict" mode mean for required checks? A: The PR branch must be up-to-date with the base branch before merging. This prevents situations where two individually-passing PRs cause failures when both are merged.
Q: How do you balance fast feedback with thorough checks? A: Run fast checks (lint, type check) first and slow checks (integration tests) in parallel. Use CI caching for dependencies. Make lint and unit tests required; make slow integration tests optional or run them only on certain paths.