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 else
);

unit-test examples, using esmock and ava for various situations

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

test('should mock local files, packages and core modules', async t => {
  const main = await esmock('../src/main.js', {
    fs: { readFileSync: () => 'give it a star' },
    stringifierpackage : o => JSON.stringify(o),
    '../src/hello.js' : {
      default : () => 'world'
    },
    '../src/util.js' : {
      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 not deleted from cache
  const doAwaitImport = await esmock.p('../awaitImportLint.js', {
    eslint : { ESLint : cfg => cfg }
  });

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

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