jest-fixture

Helpers to create file based fixtures for use with jest.

Installation & Usage

npm i jest-fixture --save-dev

import { environment, prepare, file, packageJson } from 'jest-fixture'
import { build } from '../my-build-plugin'

const [fixturePath, setCwd] = environment('build')

test('Build generates required files with modules.', async () => {
  const { dist } = prepare([
    file('index.js', "import 'imported.js'"),
    file('imported.js', "console.log('Hello World!')"),
    packageJson('build', { type: 'module' }),
  ])

  await build()

  const files = listFilesMatching('*.js.map', dist)

  // Source map file is generated.
  expect(files.length).toEqual(1)
  expect(files[0]).toEqual('index.js.map')

  const contents = contentsForFilesMatching('*.js', dist)

  // Contents of imported files included in generated file.
  expect(contents.length).toBeGreaterThan(0)
  expect(contents[0].name).toEqual('index.js')
  expect(contents[0].contents).toContain('Hello World')
})

readFile and writeFile

import { readFile, writeFile } from 'jest-fixture'

const fileContentsAsString = readFile('index.js')
const { name, version } = readFile('package.json')

// With options:
const { presets } = readFile('.babelrc', {
  // Default false, or detected from .json extension.
  json: true,
})

writeFile('index.js', `alert('Knock, knock. Who's there?')`)
writeFile('package.json', {
  name: 'my-app',
  version: '1.0.0',
})

// With options:
writeFile(
  '.babelrc',
  {
    presets: ['@babel/preset-env'],
  },
  {
    // Default false, or detected from .json extension.
    json: true,
    // Default true, will add newline if not present already.
    ensureNewLine: false,
  }
)

listFilesMatching and contentsForFilesMatching

Reads all files matching a glob pattern in a specific folder or process.cwd().

import { join } from 'path'
import { listFilesMatching, contentsForFilesMatching } from 'jest-fixture'

const files = listFilesMatching('*.js')
const sourceMapFilesInDist = listFilesMatching('*.map.js', join(process.cwd(), 'dist'))

// files === ['index.js', 'components.js']

const contents = contentsForFilesMatching('*.css')

// contents === [{ name: styles.css, contents: 'body { display: none; }' }]

wait

Wait for a number of seconds to pass.

import { wait } from 'jest-fixture'

// Waits 5 seconds.
await wait(5)

environment and prepare

Use the environment before a test suite to create a dedicated folder inside test/fixture where process.cwd is set to this folder beforeEach test and the contents are removed afterEach. Prepare will setup the passed files inside the fixturePath so these files can then be used by tests separate from the files of other test suites.

const [fixturePath, setCwd] = environment('suite')

test('Some test.', async () => {
  // fixturePath === 'test/fixture/suite'
  const { dist } = prepare([file('index.js', "console.log('hello')")])
  // dist === 'test/fixture/suite/dist'
  // test/fixture/suite/index.js created
})

file, json, packageJson and interface File

prepare expects a list of File[]s. Such a File object can be manually constructed or through one of the helpers in the second code example for commonly used files.

interface File {
  // Name of the file relative to the `fixturePath`.
  name: string
  // Optionally, write Object contents as JSON.
  json?: true
  // Contents of the file as a string or Object for JSON files.
  contents?: string | Object
  // Alternative to contents, filePath where to copy contents from.
  copy?: string
}

import { file, json, packageJson, prepare } from 'jest-fixture'

const javaScriptFile = file('index.js', "console.log('hello world')")
const jsonFile = json('phone-book.json', [
  { name: 'Bob', number: '123' },
  { name: 'John', number: '456' },
])
const packageJson = packageJson('my-plugin', {
  description: 'Meh',
  version: '1.0.0',
})

prepare([javaScriptFile, jsonFiles, packageJson])

vitest

Use the registerVitest polyfill method to use with vitest.

import { beforeEach, afterEach, vi } from 'vitest'
import { registerVitest } from 'jest-fixture'

registerVitest(beforeEach, afterEach, vi)

Or, use the following test setup code to polyfill jest globals with matching vitest globals.

import { beforeEach, afterEach, vi } from 'vitest'

global.jest = {
  spyOn: vi.spyOn,
}

global.beforeEach = beforeEach
global.afterEach = afterEach