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Reputation: 1223

Jest - Test an ES6 class

I'm learning to test my JavaScript with Jest. I have a basic project that's setup like this:

/
  /src
    myClass.js
  /tests
    myClass.test.js
  package.json

The code looks like this:

myClass.js

export class MyClass {
  constructor() {
    this.result = null;
  }

  calculate() {
    this.result = 1;
    return this.result;
  }
}

myClass.test.js

import { MyClass } from '../src/myClass';

test('Calculate', () => {
  let myObject = new MyClass();
  let result = myObject.calculate();
  expect(result).toBe(1);
});

package.json

{
    "name": "sample-project",
    "version": "0.0.1",
    "type":"module",
    "scripts": {
        "dev": "vite",
        "build": "vite build",
        "serve": "vite preview",
        "test": "jest"
    },
    "dependencies": {
        "vue": "^3.2.16",
        "vue-router": "^4.0.11"
    },
    "devDependencies": {
        "@vitejs/plugin-vue": "^1.9.3",
        "jest": "^27.3.1",
        "vite": "^2.6.4",
        "vite-plugin-html": "^2.1.1",
        "vite-plugin-singlefile": "^0.5.1"
    }
}

When I run my tests using npm run test, which just executes jest, I receive an error that says: SyntaxError: Cannot use import statement outside a module.

What am I doing wrong? How do I test MyClass from Jest?

Upvotes: 0

Views: 781

Answers (1)

Michael Haar
Michael Haar

Reputation: 711

Please follow the Babel sections in the Jest's Getting Started Guide

Simply run:

yarn add --dev babel-jest @babel/core @babel/preset-env

and create a babel.config.js file in the project root directory with the following content:

// babel.config.js
module.exports = {
  presets: [['@babel/preset-env', {targets: {node: 'current'}}]],
};

FYI: Jest is using virtual Node environments under the hood. If I remember correctly the oldest supported Node version is 10. Therefore you need to configure a source code transformer like Babel if you want to use ES6 features. (Source)

Upvotes: 2

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