Nestjs testing

Skill FilippoDeSilva/skills/skills/nestjs/nestjs-testing

Write Unit and E2E tests with Jest, mocking strategies, and database isolation in NestJS. Use when writing NestJS unit tests, E2E tests with supertest, or mock providers.From its SKILL.md

Install

npx -y skills add FilippoDeSilva/skills --skill nestjs-testing

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SKILL.md

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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