Package Exports

esmock
esmock/src/esmockLoader.mjs

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (esmock) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

esmock

esmock provides native ESM import mocking for unit tests. Use examples below as a quick-start guide or use the descriptive and friendly esmock guide here.

esmock must be used with node's experimental --loader

{
  "name": "give-esmock-a-star",
  "type": "module",
  "scripts": {
    "test-uvu": "node --loader=esmock ./node_modules/uvu/bin.js ./spec/",
    "test-ava": "ava --node-arguments=\"--loader=esmock\"",
    "test-mocha": "mocha --loader=esmock --no-warnings"
  }
}

esmock has the following signature

await esmock(
  './to/module.js', // path to target module being tested
  { ...childmocks }, // mock definitions imported by target module
  { ...globalmocks } // mock definitions imported everywhere
);

esmock demonstrated with ava unit test examples

import test from 'ava';
import esmock from 'esmock';

test('should mock local files and packages', async t => {
  const main = await esmock('../src/main.js', {
    stringifierpackage : JSON.stringify,
    '../src/hello.js' : {
      default : () => 'world',
      exportedFunction : () => 'foobar'
    }
  });

  t.is(main(), JSON.stringify({ test : 'world foobar' }));
});

test('should do global instance mocks —third parameter', async t => {
  const { getFile } = await esmock('../src/main.js', {}, {
    fs : {
      readFileSync : () => 'returns this globally';
    }
  });

  t.is(getFile(), 'returns this globally');
});

test('should mock "await import()" using esmock.p', async t => {
  // using esmock.p, mock definitions are kept in cache
  const doAwaitImport = await esmock.p('../awaitImportLint.js', {
    eslint : { ESLint : cfg => cfg }
  });

  // mock definition is there, in cache, when import is called
  t.is(await doAwaitImport('cfg'), 'cfg');

  esmock.purge(doAwaitImport); // clear cache, if you wish
});

test('should merge "default" value, when safe', async t => {
  const main = await esmock('../src/main.js');

  t.is(main(), main.default()); // use the form you prefer
});

test('should define "default" implicily, when safe', async t => {
  const mainA = await esmock('../src/exportsMain.js', {
    '../src/main.js' : () => 'mocked main' // short-hand, smaller
  });
  const mainB = await esmock('../src/exportsMain.js', {
    '../src/main.js' : { default : () => 'mocked main' }
  });

  t.is(mainA(), mainB());
});