Jest: It's impossible to reset modules when using ES6 import syntax

[DzoQiEuoi]

If you are using ES6 import syntax, there is no way to reset modules between tests. The only workaround is to put tests in different files, or switch to non-standard require syntax.

For example, the following test suite will fail due to shared state:

import { five } from 'aModule';

beforeEach() {
  jest.resetModules();
}

describe('testSuite', () => {
  test('firstTest', () => {
    five++;
    expect(five).toBe(6);
  });

  test('secondTest', () => {
    five + 2;
    expect(five).toBe(7);
  });
});

Event using the resetModules option will not reset five because the reference has already been created.

There should be an option to run each test in complete isolation.

[jwbay]

Resetting the module registry doesn't do any good if you don't re-import or re-require the module afterward. See examples at https://facebook.github.io/jest/docs/jest-object.html#jestresetmodules. I think your options are to use require or the fancy new import() syntax.

[thymikee]

Just as @jwbay said (thanks ❤️). Use require(), it's definitely not _"non-standard"_.

[xiaojingzhao]

Just as @jwbay said (thanks ❤️). Use require(), it's definitely not _"non-standard"_.

Hi, I tried require(). But it not acted as what I expected.
I have a module A

module.exports = {
  a: 3
};

And I add test file

const jestTestCase = require('utils/jest');

describe('sandbox', () => {
  beforeEach(() => jest.resetModules());

  it('the first value should be 3 ', () => {
    expect(jestTestCase.a).toEqual(3);
    jestTestCase.a = 5;
  });

  it('the second value should be 3 ', () => {
    expect(jestTestCase.a).toEqual(3);
  });
});

The second test case was failed. But what I expected is all tests should be passed.

And I tried inline require. It seems only inline require works.

describe('sandbox', () => {
  beforeEach(() => jest.resetModules());
  it('the first value should be 3 ', () => {
    const jestTestCase = require('utils/jest');
    expect(jestTestCase.a).toEqual(3);
    jestTestCase.a = 5;
  });

  it('the second value should be 3 ', () => {
    const jestTestCase = require('utils/jest');
    expect(jestTestCase.a).toEqual(3);
  });
});

But jest said they run all tests in sandbox. How to understand sandbox here?

[luciomartinez]

Just in case someone else is also lost after trying above's solution but using import. Here's a fix for it:

describe('MyTests', () => {
  let MyModule;

  beforeEach(() => {
    return import('../module/path').then(module => {
      MyModule = module;
      jest.resetModules();
    });
  });

  test('should test my module', () => {
    expect(MyModule.aMethod).not.toBeUndefined();
  });
});

Requisites: configure the babel-plugin-dynamic-import-node babel plugin.

Source: https://jestjs.io/docs/en/jest-object#jestdomockmodulename-factory-options