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Next.js 15 Fullstack (App Router + Server Actions) · Lesson

Mocking & Testing API Routes

Test Next.js Route Handlers and Server Actions in isolation by mocking the database, network calls, and external services with Jest and MSW.

Why Mock?

Tests should be fast, deterministic, and isolated. Mocking replaces slow or external dependencies — databases, payment APIs, email senders — with controllable stand-ins so a single failure does not break unrelated tests.

What to Mock

Good mock targets in a Next.js app:

  • The database client (Prisma)
  • External HTTP calls (Stripe, OpenAI)
  • Auth/session helpers

Keep the route's own logic real so you actually test it.

All lessons in this course

  1. Unit Testing Components
  2. Integration Testing Pages
  3. E2E with Playwright/Cypress
  4. Mocking & Testing API Routes
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