使用 JEST 和 Vue.js 失败“插件/预设文件不允许导出对象，只能导出函数。”

Question

Hello everyone!

i have a problem with jest. I want to test a view.js application with jest. The application is already well advanced.

I create a very simple test to understand the operation but it always returns me an error.

 FAIL  test/unit/specs/sum.test.js
 ● Test suite failed to run

  at createDescriptor (node_modules/@babel/core/lib/config/config-descriptors.js:178:11)
  at items.map (node_modules/@babel/core/lib/config/config-descriptors.js:109:50)
      at Array.map (<anonymous>)
  at createDescriptors (node_modules/@babel/core/lib/config/config-descriptors.js:109:29)
  at createPresetDescriptors (node_modules/@babel/core/lib/config/config-descriptors.js:101:10)
  at presets (node_modules/@babel/core/lib/config/config-descriptors.js:47:19)
  at mergeChainOpts (node_modules/@babel/core/lib/config/config-chain.js:320:26)
  at node_modules/@babel/core/lib/config/config-chain.js:283:7
  at buildRootChain (node_modules/@babel/core/lib/config/config-chain.js:120:22)
  at loadPrivatePartialConfig (node_modules/@babel/core/lib/config/partial.js:85:55)

Here is the state of my configuration:

package.json

The part scripts :

"scripts": {
  "dev": "webpack-dev-server --inline --progress --config build/webpack.dev.conf.js",
  "start": "npm run dev",
  "unit": "cross-env BABEL_ENV=test karma start test/unit/karma.conf.js --single-run",
  "e2e": "node test/e2e/runner.js",
  "test": "jest",
  "lint": "eslint --ext .js,.vue src test/unit test/e2e/specs",
  "build": "node build/build.js"
}

The part Jest :

"jest": {
  "moduleFileExtensions": [
    "js",
    "json",
    "vue"
  ],
  "transform": {
    ".*\\.(vue)$": "vue-jest",
    "^.+\\.js$": "<rootDir>/node_modules/babel-jest"
  },
  "moduleNameMapper": {
    "^@/(.*)$": "<rootDir>/src/$1"
  }
}

The part devDependencies :

"devDependencies": {
  "@vue/test-utils": "^1.0.0-beta.29",
  "autoprefixer": "^7.1.2",
  "babel-core": "^6.22.1",
  "babel-eslint": "^8.2.1",
  "babel-helper-vue-jsx-merge-props": "^2.0.3",
  "babel-jest": "^24.1.0",
  "babel-loader": "^7.1.1",
  "babel-plugin-istanbul": "^4.1.1",
  "babel-plugin-syntax-jsx": "^6.18.0",
  "babel-plugin-transform-runtime": "^6.22.0",
  "babel-plugin-transform-vue-jsx": "^3.5.0",
  "babel-preset-env": "^1.3.2",
  "babel-preset-stage-2": "^6.22.0",
  "babel-register": "^6.22.0",
  "chai": "^4.1.2",
  "chalk": "^2.0.1",
  "chromedriver": "^2.27.2",
  "copy-webpack-plugin": "^4.0.1",
  "cross-env": "^5.0.1",
  "cross-spawn": "^5.0.1",
  "css-loader": "^0.28.11",
  "eslint": "^4.15.0",
  "eslint-config-standard": "^10.2.1",
  "eslint-friendly-formatter": "^3.0.0",
  "eslint-loader": "^1.7.1",
  "eslint-plugin-import": "^2.7.0",
  "eslint-plugin-node": "^5.2.0",
  "eslint-plugin-promise": "^3.4.0",
  "eslint-plugin-standard": "^3.0.1",
  "eslint-plugin-vue": "^4.0.0",
  "extract-text-webpack-plugin": "^3.0.0",
  "file-loader": "^1.1.4",
  "friendly-errors-webpack-plugin": "^1.6.1",
  "html-webpack-plugin": "^2.30.1",
  "inject-loader": "^3.0.0",
  "jest": "^24.1.0",
  "karma": "^1.4.1",
  "karma-coverage": "^1.1.1",
  "karma-mocha": "^1.3.0",
  "karma-phantomjs-launcher": "^1.0.2",
  "karma-phantomjs-shim": "^1.4.0",
  "karma-sinon-chai": "^1.3.1",
  "karma-sourcemap-loader": "^0.3.7",
"karma-spec-reporter": "0.0.31",
"karma-webpack": "^2.0.2",
"mocha": "^3.2.0",
"nightwatch": "^0.9.12",
"node-notifier": "^5.1.2",
"optimize-css-assets-webpack-plugin": "^3.2.0",
"ora": "^1.2.0",
"phantomjs-prebuilt": "^2.1.14",
"portfinder": "^1.0.13",
"postcss-import": "^11.0.0",
"postcss-loader": "^2.0.8",
"postcss-url": "^7.2.1",
"rimraf": "^2.6.0",
"selenium-server": "^3.0.1",
"semver": "^5.3.0",
"shelljs": "^0.7.6",
"sinon": "^4.0.0",
"sinon-chai": "^2.8.0",
"style-loader": "^0.20.3",
"stylus": "^0.54.5",
"stylus-loader": "^3.0.2",
"uglifyjs-webpack-plugin": "^1.1.1",
"url-loader": "^0.5.8",
"vue-jest": "^3.0.3",
"vue-loader": "^13.3.0",
"vue-style-loader": "^3.0.1",
"vue-template-compiler": "^2.5.2",
"webpack": "^3.6.0",
"webpack-bundle-analyzer": "^2.9.0",
"webpack-dev-server": "^2.9.1",
"webpack-merge": "^4.1.0"

} }

The function to be tested

The file name sum.js

export default function sum (a, b) {
  return a + b
}

File that must test the function

The file sum.test.js

import sum from '../../../src/components/sum'

describe('sum', () => {
  it('create sum of 2 numbrers', () => {
    expect(sum(15, 8)).toBe(23)
  })
})

The file structure and the like this:

src
-components
--sum.js
test
-unit
--specs
---sum.test.js

Answer 1

Never had your problem so I don't know if this will help, but:

"^.+\\.js$": "<rootDir>/node_modules/babel-jest"

This line troubles me. If I install babel-jest locally in my node_modules, under node_modules/babel-jest/ there is a build folder with and index.js . There is no executable file under node_modules/babel-jest . maybe that's the root of your problem.

I would try with:

"^.+\\.js$": "babel-jest"

If that does not work, I would try:

"^.+\\.js$": "<rootDir>/node_modules/babel-jest/build"

Good luck!