Jest can't test React state

Question

My testing with jest failing when I add state to the component. Im trying to get s snaphot, and without state everything works so I think probles in reading latest react "style" of declaring the state. I think Im missing some kind of babel library or something.

Jest:

This usually means that you are trying to import a file which Jest cannot parse, e.g. it's not plain JavaScript. By default, if Jest sees a Babel config, it will use that to transform you r files, ignoring "node_modules". Here's what you can do: To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config. If you need a custom transformation specify a "transform" option in your config. If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option. You'll find more details and examples of these config options in the docs: https://jestjs.io/docs/en/configuration.html

Console:

> test@0.1.0 test C:\test
> jest

 FAIL  src/App.test.js
  ? Test suite failed to run

    C:/test/src/App.js: Unexpected token (5:6)

      Jest encountered an unexpected token

      Details:
        3 |
        4 | class App extends Component {
      > 5 |     state={
          |          ^
        6 |             value: 'value'
        7 |     }
        8 |   render() {

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        8.307s
Ran all test suites.
npm ERR! Test failed.  See above for more details.

package.json

{
  "name": "boilertest",
  "version": "0.1.0",
  "private": true,
  "babel": {
    "presets": [
      "es2015",
      "react"
    ]
  },
  "jest": {
    "snapshotSerializers": [
      "<rootDir>/node_modules/enzyme-to-json/serializer"
    ],
    "moduleNameMapper": {
      "^.+\\.(css|scss)$": "identity-obj-proxy"
    }
  },
  "dependencies": {
    "axios": "^0.18.0",
    "bootstrap": "^4.1.3",
    "react": "^16.6.0",
    "react-dom": "^16.6.0",
    "react-router-dom": "^4.3.1",
    "react-scripts": "2.0.5"
  },
  "devDependencies": {
    "babel-core": "^6.26.3",
    "babel-jest": "^23.6.0",
    "babel-preset-es2015": "^6.24.1",
    "babel-preset-react": "^6.24.1",
    "enzyme": "^3.7.0",
    "enzyme-adapter-react-16": "^1.6.0",
    "enzyme-to-json": "^3.3.4",
    "identity-obj-proxy": "^3.0.0",
    "jest": "^23.6.0"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "jest --watch",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "browserslist": [
    ">0.2%",
    "not dead",
    "not ie <= 11",
    "not op_mini all"
  ]
}

Thank you!

Answer 1

You need to add what danmakenoise suggested, npm i babel-plugin-transform-class-properties --save. This plugin transforms the experimental state = {} into constructor(){} syntax, prior to running Jest.

Once you've added this plugin, you need to update your .babelrc file to include the plugin: "plugins": ["transform-class-properties"].

Answer 2

Looks like you just need to install https://www.npmjs.com/package/babel-plugin-transform-class-properties

Defining the state object like that is not in the current standard, and this will transpile it for you!