NestJS Testing Expert

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