Use jest to test typescript

use-jest-in-ts-project.md

1. Add devDependencies: @babel/preset-env, @babel/preset-typescript, @types/jest, jest
2. Create babel.config.js file:

module.exports = {
  presets: [
    [
      '@babel/preset-env', { targets: { node: 'current' } }
    ],
    '@babel/preset-typescript',
  ],
};

3. Add scripts: "test": "jest"