JSPM – esmock@1.8.0

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

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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 is used with node's --loader

{
  "name": "give-esmock-a-star",
  "type": "module",
  "scripts": {
    "test": "node --loader=esmock --test",
    "test-tap": "NODE_OPTIONS=--loader=esmock tap",
    "test-uvu": "NODE_OPTIONS=--loader=esmock uvu spec",
    "test-ava": "NODE_OPTIONS=--loader=esmock ava",
    "test-mocha": "mocha --loader=esmock"
  }
}

esmock has the below 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 examples

import test from 'node:test'
import assert from 'node:assert/strict'
import esmock from 'esmock'

test('should mock local files and packages', async () => {
  const main = await esmock('../src/main.js', {
    stringifierpackage: JSON.stringify,
    '../src/hello.js': {
      default: () => 'world',
      exportedFunction: () => 'foo'
    }
  })

  assert.strictEqual(main(), JSON.stringify({ test: 'world foo' }))
})

test('should do global instance mocks —third param', async () => {
  const { getFile } = await esmock('../src/main.js', {}, {
    fs: {
      readFileSync: () => 'returns this globally'
    }
  })

  assert.strictEqual(getFile(), 'returns this globally')
})

test('should mock "await import()" using esmock.p', async () => {
  // using esmock.p, mock definitions are kept in cache
  const doAwaitImport = await esmock.p('../awaitImportLint.js', {
    eslint: { ESLint: cfg => cfg }
  })

  // mock definition is returned from cache, when import is called
  assert.strictEqual(await doAwaitImport('cfg'), 'cfg')
  // a bit more info are found in the descriptive guide
})

// a "partial mock" merges the new and original definitions
test('should suppport partial mocks', async () => {
  const pathWrap = await esmock('../src/pathWrap.js', {
    path: { dirname: () => '/path/to/file' }
  })

  // an error, because path.basename was not defined
  await assert.rejects(async () => pathWrap.basename('/dog.png'), {
    name: 'TypeError',
    message: 'path.basename is not a function'
  })

  // use esmock.px to create a "partial mock"
  const pathWrapPartial = await esmock.px('../src/pathWrap.js', {
    path: { dirname: () => '/home/' }
  })

  // no error, because "core" path.basename was merged into the mock
  assert.deepEqual(pathWrapPartial.basename('/dog.png'), 'dog.png')
  assert.deepEqual(pathWrapPartial.dirname(), '/home/')
})