nestjs-testing

name	nestjs-testing
description	Unit and E2E testing with Jest, mocking strategies, and database isolation. Use when writing NestJS unit tests, E2E tests with supertest, or mock providers. (triggers: **/*.spec.ts, test/**/*.e2e-spec.ts, Test.createTestingModule, supertest, jest, beforeEach)

NestJS Testing

Priority: P2 (MAINTENANCE)

Structure

src/**/*.spec.ts      # Unit tests (isolated logic)
test/**/*.e2e-spec.ts # E2E tests (full app flows)

Unit Testing

• Setup: Use Test.createTestingModule() with mocked providers
• Mocks: Mock all dependencies via { provide: X, useValue: mockX }
• Pattern: AAA (Arrange-Act-Assert)
• Cleanup: Call jest.clearAllMocks() in afterEach

E2E Testing

• Database: Use real test DB (Docker). Never mock DB in E2E.
• Cleanup: Mandatory. Use transaction rollback or TRUNCATE in afterEach.
• App Init: Create app in beforeAll, close in afterAll
• Guards: Override via .overrideGuard(X).useValue({ canActivate: () => true })

Strict TypeScript (MANDATORY)

• No any: Use typed objects, jest.Mocked<T>, or as unknown as T. Never as any.
• No eslint-disable: Fix underlying type issue. No exceptions.
• Verify DTO shapes: Read actual DTO class before writing mock data.
• Cast Jest matchers: Nested expect.anything() → expect.anything() as unknown.
• No unused vars: Only declare variables if referenced in assertions or setup.

Anti-Patterns

• No Private Tests: Test via public methods, not service['privateMethod']. When coverage requires it, use typed helper (see strict-typescript reference).
• No DB Mocks in E2E: Use real DB with cleanup. Mocks defeat E2E purpose.
• No Shared State: Call jest.clearAllMocks() in afterEach. Random failures otherwise.
• No Resource Leaks: Always close app and DB in afterAll.

References

Setup examples, mocking patterns, E2E flows, test builders, coverage config: references/patterns.md

Strict-TypeScript patterns (Jest matchers, mock typing, DTO verification): references/strict-typescript-testing.md