Jest Presets

Unified Jest testing configuration for Node.js workspaces with consistent test execution across the monorepo

Overview

@workspace/jest-presets provides unified Jest configuration for Node.js workspaces in the monorepo. This ensures consistent test execution and coverage reporting for API and server-oriented packages.

Features

Shared Presets - Consistent testing configuration for Node.js environments
Node.js Preset - For server-side, API, and package testing
TypeScript Support - Built-in TypeScript test support via ts-jest
Coverage Reporting - Integrated coverage tracking

Project Structure

packages/jest-presets/
├── node/
│   └── jest-preset.js   # Node.js/server testing configuration
├── package.json         # Dependencies
└── README.md           # Package documentation

Available Presets

Node.js Preset

For server-side code, Express APIs, backend packages, and utilities:

// jest.config.js
const preset = require("@workspace/jest-presets/node");

module.exports = preset;

Configuration includes:

Jest environment: node
TypeScript and TSX support via ts-jest
Path alias mapping for @workspace/utils packages
Module extensions: .ts, .tsx, .js, .jsx, .json, .node
Ignores test fixtures, node_modules, and dist directories

Usage

Web workspaces use Vitest via Vitest Presets. Keep Jest presets for API/server workspaces unless you are intentionally migrating test runners.

Running Tests

Run all tests across the monorepo:

pnpm test

Run tests for a specific workspace:

pnpm test --filter=auth
pnpm test --filter=db

Watch mode for development:

pnpm test -- --watch

Coverage Reports

Generate coverage reports:

pnpm test

Coverage output goes to the coverage/ directory in each workspace.

File Structure for Testing

Recommended test file organization:

src/
├── utils/
│   ├── format.ts
│   └── format.test.ts
├── services/
│   ├── api.ts
│   └── api.test.ts
└── helpers/
    ├── helpers.ts
    └── helpers.test.ts

Writing Tests

Example: Utility Function Test

import { capitalize } from "@workspace/utils/helpers";

describe("capitalize", () => {
  it("capitalizes the first letter", () => {
    expect(capitalize("hello")).toBe("Hello");
  });

  it("handles empty strings", () => {
    expect(capitalize("")).toBe("");
  });
});

Example: API Function Test

import { getUserById } from "@/services/user";

describe("getUserById", () => {
  it("returns user data", async () => {
    const user = await getUserById("123");
    expect(user.id).toBe("123");
  });

  it("throws on invalid ID", async () => {
    await expect(getUserById("invalid")).rejects.toThrow();
  });
});

Customizing Jest Configuration

To customize Jest for a specific workspace, extend the preset:

const preset = require("@workspace/jest-presets/node");

module.exports = {
  ...preset,
  testPathIgnorePatterns: ["node_modules", "dist/"],
  collectCoverageFrom: [
    "src/**/*.{ts,tsx}",
    "!src/**/*.d.ts",
    "!src/**/*.test.{ts,tsx}",
  ],
  coverageThreshold: {
    global: {
      branches: 70,
      functions: 70,
      lines: 70,
      statements: 70,
    },
  },
};

Key Scripts

Run from the monorepo root:

Command	Purpose
`pnpm test`	Run all workspace tests

Run from individual workspaces (e.g., apps/api, packages/utils):

Command	Purpose
`pnpm test`	Run tests with coverage reporting
`pnpm test -- --watch`	Watch mode for development

Best Practices

Write Descriptive Test Names

// ✓ Good
it("returns user when ID is valid", () => {
  // implementation
});

// ✗ Vague
it("works", () => {
  // implementation
});

Test Edge Cases

describe("calculateTotal", () => {
  it("sums positive numbers", () => {
    expect(calculateTotal([1, 2, 3])).toBe(6);
  });

  it("handles empty array", () => {
    expect(calculateTotal([])).toBe(0);
  });

  it("handles negative numbers", () => {
    expect(calculateTotal([1, -2])).toBe(-1);
  });
});

Use Async/Await

// ✓ Good
it("fetches user data", async () => {
  const user = await fetchUser(123);
  expect(user.name).toBe("John");
});

// ✓ Also good with done callback
it("fetches user data", (done) => {
  fetchUser(123).then((user) => {
    expect(user.name).toBe("John");
    done();
  });
});

Troubleshooting

Tests Not Found

# Ensure test files follow naming convention
# Should be *.test.ts or *.spec.ts

# Check jest.config.ts includes correct patterns

TypeScript Errors

# Regenerate types
pnpm check-types

# Clear Jest cache
pnpm test --clearCache

Coverage Thresholds

If tests pass but coverage thresholds fail, add more test cases for untested code paths.

For more details on Jest configuration, see the Jest documentation.

Jest Presets

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