| name | NestJS Jest Testing |
| description | Complete guide for setting up Jest unit tests, e2e tests, Stryker mutation testing, jest-it-up coverage bumping, tsx smoke tests, and reusable GitHub Actions verify workflows in NestJS TypeScript projects. |
NestJS Jest Testing
Overview
This skill covers the full test setup for NestJS TypeScript projects using Jest + ts-jest, with separate configs for unit and e2e tests, Stryker for mutation coverage (80% break threshold), jest-it-up for auto-bumping coverage thresholds.
Key Concepts
- ts-jest: Transforms TypeScript for Jest without a separate compile step; uses the project's tsconfig.json
- Unit tests: Use constructor injection mocks — no import mocking, dependencies passed via DI
- E2e tests: Boot the full NestJS module with
Test.createTestingModule({ imports: [AppModule] }) + supertest
- Stryker: Runs Jest on mutated code;
break: 80 exits with code 1 if mutation score drops below 80%
- jest-it-up: Reads
coverage/coverage-summary.json after tests and bumps jest.config thresholds upward
Documentation & References
Recommended Libraries & Tools
| Name | Purpose | Maturity | Notes |
|---|
jest | Test runner | Stable (v29.7) | Core testing framework |
ts-jest | TS transformer for Jest | Stable (v29.2) | CommonJS preset for this project |
@types/jest | Type declarations for Jest | Stable (v29.5) | Required for TypeScript tests |
@nestjs/testing | NestJS test module | Stable (v11) | createTestingModule, overrideProvider |
supertest | HTTP assertions for e2e | Stable (v7) | Works with NestJS app instance |
@types/supertest | Type declarations | Stable (v6) | Required for TypeScript e2e tests |
jest-it-up | Auto-bump coverage thresholds | Stable (v4.0.1) | Requires json-summary coverageReporter |
@stryker-mutator/core | Mutation testing engine | Stable (v8) | Core package |
@stryker-mutator/jest-runner | Jest integration for Stryker | Stable (v8) | Matches project's jest setup |
@stryker-mutator/typescript-checker | Type-safe mutation filtering | Stable (v8) | Filters type-invalid mutants before test run |
Recommended Stack
Use jest + ts-jest (CommonJS preset) for both unit and e2e tests, with separate config files. Use @nestjs/testing for all test modules. Add jest-it-up as a posttest script for unit tests only. Use @stryker-mutator with jest runner and TypeScript checker for mutation testing.
Patterns & Best Practices
Pattern 1: Unit Test with Constructor Injection Mocks
When to use: Testing any NestJS service with injected dependencies. No import mocking — pass fake implementations via constructor.
Trade-offs: Requires services to be refactored to inject external clients (Pool, GraphQLClient) if they create them internally.
import { QueueProcessorService } from '../queue-processor.service'
const mockPgmqService = {
readMessage: jest.fn(),
deleteMessage: jest.fn(),
}
const mockConsentClient = {
saveConsent: jest.fn(),
}
describe('QueueProcessorService', () => {
let service: QueueProcessorService
beforeEach(() => {
jest.clearAllMocks()
service = new QueueProcessorService(
mockPgmqService as any,
mockConsentClient as any,
)
})
it('processes a message successfully', async () => {
mockPgmqService.readMessage.mockResolvedValueOnce({ msg_id: '1', message: {} })
})
})
Pattern 2: E2e Test with AppModule and supertest
When to use: Integration testing the full NestJS application over HTTP.
Critical: Set process.env vars in a setupFiles script before the module boots — configify validates at init time, before overrideProvider() takes effect. See E2E Testing with Configify in the configify skill.
import { Test, TestingModule } from '@nestjs/testing'
import { INestApplication } from '@nestjs/common'
import * as request from 'supertest'
import { AppModule } from '../src/app.module'
describe('AppController (e2e)', () => {
let app: INestApplication
beforeAll(async () => {
const moduleFixture: TestingModule = await Test.createTestingModule({
imports: [AppModule],
})
.overrideProvider(SomeService)
.useValue(mockSomeService)
.compile()
app = moduleFixture.createNestApplication()
await app.init()
})
afterAll(async () => {
await app.close()
})
it('/health (GET)', () =>
request(app.getHttpServer()).get('/health').expect(200))
})
Pattern 4: Separate Jest Configs (Unit vs E2e)
When to use: Always — unit and e2e tests have different roots, patterns, setup files, and timeouts.
import type { Config } from 'jest'
const config: Config = {
preset: 'ts-jest',
testEnvironment: 'node',
testMatch: ['**/__tests__/**/*.spec.ts'],
collectCoverage: true,
collectCoverageFrom: [
'src/**/*.ts',
'!src/**/__tests__/**',
'!src/generated/**',
'!src/main.ts',
'!src/**/*.module.ts',
],
coverageDirectory: 'coverage',
coverageReporters: ['text', 'lcov', 'html', 'json-summary'],
coverageProvider: 'v8',
coverageThreshold: {
global: { branches: 80, functions: 80, lines: 80, statements: 80 },
},
}
export default config
import type { Config } from 'jest'
const config: Config = {
preset: 'ts-jest',
testEnvironment: 'node',
testMatch: ['**/tests/**/*.spec.ts'],
setupFiles: ['./tests/e2e-env-setup.ts'],
testTimeout: 30000,
}
export default config
Stryker Configuration
{
"testRunner": "jest",
"coverageAnalysis": "perTest",
"jest": {
"projectType": "custom",
"configFile": "jest.config.ts"
},
"checkers": ["typescript"],
"tsconfigFile": "tsconfig.json",
"mutate": [
"src/**/*.ts",
"!src/**/__tests__/**/*.ts",
"!src/generated/**",
"!src/main.ts",
"!src/**/*.module.ts"
],
"reporters": ["html", "text", "progress"],
"thresholds": { "high": 80, "low": 60, "break": 80 }
}
break: 80 means Stryker exits with code 1 if mutation score drops below 80%, blocking CI.
Package.json Scripts
{
"scripts": {
"test:unit": "jest --config jest.config.ts",
"posttest:unit": "jest-it-up",
"test:e2e": "jest --config jest.e2e.config.ts",
"test:mutation": "stryker run",
"test:smoke-local": "bash smoke-tests/run-smoke-tests-local.sh",
"test": "npm run test:unit && npm run test:e2e && npm run test:smoke-local"
}
}
Note: jest-it-up runs as posttest:unit (not posttest) to avoid running after e2e/smoke.
Similar Implementations
NestJS official CLI generated test setup
- Source: NestJS CLI
nest new scaffold
- Approach: Separate
jest (unit) and jest-e2e.json (e2e) configs, test/ folder for e2e
- Applicability: Direct match — this skill follows the same conventions
Stryker Node.js guide
Sources & Verification
Changelog
| Date | Changes |
|---|
| 2026-04-23 | Initial creation for task: Add unit tests and smoke tests |
