Jest Enzyme测试抛出意外的令牌错误

Question

When I run the test, it thorws "unexpected token error at the code:

const wrapper = shallow(<WelcomeMessage/>");

The error is thrown at "(<". I have looked at a number of answers from stackoverflow and github but somehow I still cannot get it to work.

I have written jest tests. This is my first time writing a test case using enzyme and react. So I am not familar with the setup. I have installed: babel jest, react-dom, babel-plugin-transform-export-extensions, enzyme-adapter-react-16, react-test-renderer, @babel/preset-env, and @babel/core

{
  "private": true,
  "version": "0.0.0",
  "name": "example-jquery",
  "devDependencies": {
    "@babel/core": "*",
    "@babel/preset-env": "^7.4.4",
    "babel-jest": "^24.8.0",
    "babel-plugin-transform-export-extensions": "^6.22.0",
    "enzyme": "^3.9.0",
    "enzyme-adapter-react-16": "^1.12.1",
    "jest": "^24.8.0",
    "jest-dom": "^3.1.4",
    "jest-useragent-mock": "0.0.3"
  },
  "dependencies": {
    "jest-puppeteer": "^4.1.1",
    "jquery": "^3.4.1",
    "jsdom": "^15.0.0",
    "puppeteer": "^1.15.0",
    "react": "^16.8.6",
    "react-dom": "^16.8.6",
    "react-test-renderer": "^16.8.6"
  },
  "scripts": {
    "test": "jest --verbose"
  },
  "jest": {
    "transform": {
      "^.+\\.jsx?$": "babel-jest"
    }
  }
}

module.exports = {
  preset: 'jest-puppeteer',
  "bail": 0,
  setupFiles: ['<rootDir>/enzyme.config.js'],
  moduleFileExtensions: ['js', 'json', 'jsx'],
  transformIgnorePatterns: ['<rootDir>/node_modules/']
}

const Enzyme = require('enzyme');
const Adapter = require('enzyme-adapter-react-16');

Enzyme.configure({ adapter: new Adapter() });

{
  "presets": ["@babel/preset-env"],
  "plugins": ["transform-export-extensions"],
  "only": [
        "./**/*.js",
        "node_modules/jest-runtime"
      ]
}

import React from 'react';
import { shallow } from 'enzyme';

// Components
import WelcomeMessage from './WelcomeMessage';

function setup() {
  const props = {
    imgPath: 'some/image/path/to/a/mock/image',
  };
  const wrapper = shallow(<WelcomeMessage />);
  return { wrapper, props };
}

describe('WelcomeMessage Test Suite', () => {
  it('Should have an image', () => {
    const { wrapper } = setup();
    expect(wrapper.find('img').exists()).toBe(true);
  });
});

Answer 1

This line:

<WelcomeMessage />

is JSX which "just provides syntactic sugar for the React.createElement function" .

Since JSX isn't actually valid JavaScript code it must be compiled into React.createElement calls.

This is done by the Babel plugin @babel/plugin-transform-react-jsx which is included as part of @babel/preset-react .

Add @babel/preset-react to your Babel config and that should resolve the issue.