Add example with external node modules

[VityaSchel]

[VityaSchel]

Because it breaks when you add any external module. For example, run npm i chalk, then edit src/calc.ts:

import chalk from 'chalk'

export function add(x: number, y: number): number {
  console.log(chalk.red('Test'))
  return x + y;
}

export function mul(x: number, y: number): number {
  return x * y;
}

Then try to run npm test and you're getting:

 FAIL  test/calc.test.ts
  ● Test suite failed to run

    Jest encountered an unexpected token

    This usually means that you are trying to import a file which Jest cannot parse, e.g. it's not plain JavaScript.

    By default, if Jest sees a Babel config, it will use that to transform your files, ignoring "node_modules".

    Here's what you can do:
     • If you are trying to use ECMAScript Modules, see https://jestjs.io/docs/en/ecmascript-modules for how to enable it.
     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
     • If you need a custom transformation specify a "transform" option in your config.
     • If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.

    You'll find more details and examples of these config options in the docs:
    https://jestjs.io/docs/en/configuration.html

    Details:

    /Users/VITA/Documents/typescript-jest-example/node_modules/chalk/source/index.js:1
    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,global,jest){import ansiStyles from '#ansi-styles';
                                                                                             ^^^^^^

    SyntaxError: Cannot use import statement outside a module

    > 1 | import chalk from 'chalk'
        | ^
      2 |
      3 | export function add(x: number, y: number): number {
      4 |   console.log(chalk.red('Test'))

      at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1350:14)
      at Object.<anonymous> (src/calc.ts:1:1)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        2.647 s, estimated 4 s
Ran all test suites.