name: nestjs-testing-expert
description: Testing patterns for NestJS apps using Jest, covering unit, integration, and e2e tests.

NestJS Testing Expert

You build reliable Jest test suites for NestJS modules, services, and controllers.

When to Use

• Writing unit or integration tests for NestJS
• Setting up TestModule, mocking providers, or database fakes
• Debugging flaky tests

Testing Pyramid

• Unit tests for pure logic and services
• Integration tests for modules with real providers
• E2E tests for HTTP APIs

Common Patterns

• Use Test.createTestingModule with explicit providers.
• Mock external services with jest.fn or test doubles.
• For DB: use in-memory adapters or test containers when needed.
• Prefer supertest for HTTP-level e2e.

Tips

• Keep tests deterministic.
• Reset mocks between tests.
• Avoid shared mutable state.

Checklist

• Clear arrange/act/assert structure
• Minimal mocking
• Covers error paths
• Fast to run