Jest Setup

This guide covers setting up typesugar with Jest.

Installation

npm install --save-dev jest ts-jest @types/jest @typesugar/transformer ts-patch

Configuration

jest.config.js

/** @type {import('ts-jest').JestConfigWithTsJest} */
module.exports = {
  preset: "ts-jest",
  testEnvironment: "node",
  transform: {
    "^.+\\.tsx?$": [
      "ts-jest",
      {
        astTransformers: {
          before: [
            {
              path: "@typesugar/transformer",
              options: { verbose: false },
            },
          ],
        },
      },
    ],
  },
};

jest.config.ts (TypeScript)

import type { JestConfigWithTsJest } from "ts-jest";

const config: JestConfigWithTsJest = {
  preset: "ts-jest",
  testEnvironment: "node",
  transform: {
    "^.+\\.tsx?$": [
      "ts-jest",
      {
        astTransformers: {
          before: [
            {
              path: "@typesugar/transformer",
              options: { verbose: false },
            },
          ],
        },
      },
    ],
  },
};

export default config;

ESM Support

For ESM projects:

/** @type {import('ts-jest').JestConfigWithTsJest} */
module.exports = {
  preset: "ts-jest/presets/default-esm",
  testEnvironment: "node",
  extensionsToTreatAsEsm: [".ts"],
  moduleNameMapper: {
    "^(\\.{1,2}/.*)\\.js$": "$1",
  },
  transform: {
    "^.+\\.tsx?$": [
      "ts-jest",
      {
        useESM: true,
        astTransformers: {
          before: [
            {
              path: "@typesugar/transformer",
              options: {},
            },
          ],
        },
      },
    ],
  },
};

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "CommonJS",
    "moduleResolution": "Node",
    "esModuleInterop": true,
    "plugins": [{ "name": "typesugar/language-service" }, { "transform": "@typesugar/transformer" }]
  }
}

Typechecking

Jest with ts-jest provides full typechecking:

• Type errors are reported during test runs
• All macro types are fully supported
• No strict option needed — typechecking is built-in

Writing Tests

// src/utils.test.ts
import { comptime } from "typesugar";
import { derive, Eq } from "@typesugar/derive";

describe("comptime", () => {
  it("evaluates at compile time", () => {
    const value = comptime(Math.pow(2, 10));
    expect(value).toBe(1024);
  });
});

@derive(Eq)
class User {
  constructor(
    public id: number,
    public name: string
  ) {}
}

describe("derive", () => {
  it("generates equals", () => {
    const u1 = new User(1, "Alice");
    const u2 = new User(1, "Alice");
    expect(u1.equals(u2)).toBe(true);
  });
});

Running Tests

# Run all tests
npx jest

# Watch mode
npx jest --watch

# With coverage
npx jest --coverage

package.json Scripts

{
  "scripts": {
    "test": "jest",
    "test:watch": "jest --watch",
    "test:coverage": "jest --coverage"
  }
}

Next.js Projects

For Next.js with Jest:

// jest.config.js
const nextJest = require("next/jest");

const createJestConfig = nextJest({ dir: "./" });

const customJestConfig = {
  testEnvironment: "jest-environment-jsdom",
  transform: {
    "^.+\\.tsx?$": [
      "ts-jest",
      {
        astTransformers: {
          before: ["@typesugar/transformer"],
        },
      },
    ],
  },
};

module.exports = createJestConfig(customJestConfig);

Troubleshooting

"Cannot find module" errors

1. Check moduleNameMapper configuration
2. Ensure path aliases match tsconfig.json

Macros not expanding

1. Verify astTransformers.before is configured
2. Check that @typesugar/transformer is in dependencies
3. Clear Jest cache: npx jest --clearCache

Type errors

1. Add language service plugin to tsconfig.json
2. Use @ts-jest comments for Jest-specific typing

Slow tests

1. Use --maxWorkers=1 for debugging
2. Enable ts-jest cache: isolatedModules: true

transform: {
  "^.+\\.tsx?$": [
    "ts-jest",
    {
      isolatedModules: true,
      astTransformers: {
        before: ["@typesugar/transformer"],
      },
    },
  ],
},

Alternative: Vitest

Consider Vitest as an alternative. It's faster, has better ESM support, and works seamlessly with the Vite plugin.

Next Steps

• Editor Setup
• Troubleshooting