Testing ES6 class with Jest throws 'not a constructor' error

Question

I found a similar problem here, but there doesn't seem to be an answer.

I'm trying to test an ES6 class using Jest, like so:

// src/myclass.js
export default class MyClass {
    constructor(options) {
        // currently this is empty while I debug this problem
    }
}

and the test:

// test/myclass.test.js
import { MyClass } from '../src/myclass.js';

describe("Test Constructor", () => {

    test("doesn't throw error when constructed", async () => {
        expect(() => {
            const testMyClass = new MyClass();
        }).not.toThrowError();
    }

});

When I run the test, Jest throws an error saying:

TypeError: _myClass.MyClass is not a constructor

My best guess is that this is an issue with the babel config, but I can't seem to figure it out. If I change MyClass to a function instead of a class and drop the export/import (i.e., the pre-class way of doing things) then it works as expected.

Here's my config in package.json:

"devDependencies": {
    "@babel/core": "^7.1.2",
    "@babel/preset-env": "^7.1.0",
    "babel-core": "^7.0.0-bridge.0",
    "gulp": "^3.9.1",
    "gulp-babel": "^8.0.0",
    "gulp-jest": "^4.0.2",
    "gulp-rename": "^1.4.0",
    "gulp-uglify": "^3.0.1",
    "jest": "^23.6.0",
    "jest-cli": "^23.6.0",
    "pump": "^3.0.0",
    "regenerator-runtime": "^0.12.1"
  },
  "babel": {
    "presets": [
      "@babel/preset-env"
    ]
  },
  "jest": {
    "testPathIgnorePatterns": [
      "<rootDir>/node_modules/",
      "<rootDir>/test/._*.test.js"
    ],
    "testEnvironment": "jsdom",
    "setupFiles": [
      "<rootDir>/src/myclass.es6.js"
    ]
  }

Answer 1

Your import and export syntaxes do not match. You'll need to change one or the other for this to work. If you want to use the default export, eg:

export default class MyClass { ... }

Then the corresponding import is:

import MyClass from '../src/myclass.js'

---

Or if you'd like to continue using the same import syntax, then remove the 'default' when exporting:

export class MyClass { ... }

Then:

import { MyClass } from '../src/myclass.js'