Day 35 - Contract Testing & Retrospective

Date: 2025-10-24 (Friday)
Status: “Done”

Lecture Notes

Contract Testing with Schemathesis

  • Run schemathesis run --checks all --workers 4 --url http://127.0.0.1:8000/openapi.yaml to auto-generate tests.
  • Schemathesis explores random scenarios (happy paths, edge cases, missing fields).
  • Ensures the backend doesn’t break the schema when the frontend switches to the real API.

Benefits

  • Eliminates the need to handcraft complex test cases.
  • Reduces mismatch risk after refactors.
  • Acts as a quality gate inside the CI pipeline.

Mistakes & Fixes

Mistake Root Cause Fix
Added both error.tsx and not-found.tsx Redundant handling Keep only not-found.tsx
Used --base-url in Schemathesis Wrong CLI option Use the correct --url flag
Timeout on /openapi.json CORS or slow resp Point Schemathesis to the YAML file
Over-engineered backend Too many files early Start simple and refactor later

Validated Workflow

1. Define Contract (OpenAPI)
2. Mock API (Prism)
3. Build Frontend with mock data
4. Implement Backend according to the spec
5. Switch to the real API
6. Contract Testing (Schemathesis)
  • Enables frontend and backend teams to work in parallel.
  • Reduces conflicts, accelerates demos, and keeps quality stable.

Key Insights

  1. Contract-first development keeps specs aligned and shrinks integration bugs.
  2. Vertical slices make it possible to release in increments and gather early feedback.
  3. Automation (Prism, Schemathesis) cuts manual testing effort.
  4. Start simple and refactor gradually as scope grows.

Hands-On Labs

  • Run Schemathesis with the latest spec and capture the results.
  • Refresh the README workflow so the whole team can follow it.
  • Prepare the backlog for the next vertical slice based on demo feedback.