Jest: Jest blow up when used with `export * from 'something'`

[tals]

When a Jest test imports a module that includes:

// src/__tests__/test.js
import '../index.js'

// src/index.js
export * from './something';

// src/something.js
export function dog() { console.log('hello this is dog'); }

Jest will blow up with

 FAIL  __tests__/test.js
Runtime Error
TypeError: Cannot redefine property: __esModule
    at Function.defineProperty (native)

The reason for this is that Jest's mocking is slightly inaccurate, and this interacts badly with Babel's module system.

A Babel ES6 module defines:

// build/stuff.js
Object.defineProperty(exports, "__esModule", {
  value: true
});

exports.dog = dog;
function dog() {
  console.log('hello this is dog');
}

export * from './stuff' is implemented as:

// build/index.js
Object.keys(_stuff).forEach(function (key) {
  if (key === "default") return;
  Object.defineProperty(exports, key, {
    enumerable: true,
    get: function get() {
      return _stuff[key];
    }
  });
});

In Node this is fine, because Object.keys(_stuff) return ["dog"]

However when you're collecting the object props, you don't keep track if it's enumerable.

You first get the slots with getSlots():

> getSlots(component)
< ["__esModule", "dog"]

But when collecting the metadata with getMetadata() only the property value is considered. The property descriptor is ignored.
So for __esModule, we get:

> mockMetadata.members.__esModule
Object
    type: "constant"
    value: true

and thats gets placed in the mock.
At this point, Object.keys(_stuff) returns ["__esModule", "dog"], which causes the redefine error.

[timReynolds]

Related to issue #872

[cpojer]

Until this is fixed I recommend unmocking the other module in question. Personally I would probably always recommend explicitly listing everything a module exports if you'd like to iterate over them but this should still work with Jest.

[coopy]

Great bug report, @tals! I was banging my head against this, and didn't realize that it's got to do with Jest mocking: https://github.com/coopy/esmodule-dupe-definition/

I will unmock my problematic module in question.

[lennerd]

Another workaround till this is fixed is to create a mock file:

// src/__tests__/test.js
import '../index.js'

// src/index.js
export * from './dog';

export function cat() { console.log('hello this is cat'); } 

// src/dog.js
export function dog() { console.log('hello this is dog'); }

// src/__mocks__/index.js
module.exports = {
  ...jest.genMockFromModule('../index'),
  ...jest.genMockFromModule('../dog')
};

[AdrienLemaire]

@lennerd, I tried your example (exactly identical, except root dir is app/ instead of src/), and it fails

using Jest CLI v13.2.3, jasmine2, babel-jest

[lennerd]

@Fandekasp What version of Babel do you use?

[AdrienLemaire]

I'm using [email protected] and [email protected]

[cpojer]

Woah, I didn't realize babel-jest would even work with babel 5. We don't really support it any more…

[lennerd]

Yes, maybe thats the reason. I use [email protected] and [email protected].

[AdrienLemaire]

It looks like react-native 0.23.1 doesn't support babel 6... We'll have to upgrade our repo to get jest tests work with export.

Thank you for your super fast support!

[cpojer]

This will be fixed in the next release this week. Sorry about the issue.

[le0nik]

Has there been a release that fixed it?

Still seeing this issue with this type of module

plugins/index.js

import * as logger from './loggerPlugin';
import * as webApi from './webApiPlugin';

export {
  logger,
  webApi,
};

It's consumed like this:

import * as plugins from './plugins'`
// plugins.__esModule is enumerable although commonjs transform is NOT in loose mode

For now I have to use this mock as a workaround(which also triggers duplicate mocks warning, but that's another issue).

plugins/__mocks__/index.js

const _ = require('lodash');
const source = require.requireActual('../index');
const fixedSource = _.omit(source, '__esModule');

// See https://github.com/facebook/jest/issues/880
Object.defineProperty(fixedSource, '__esModule', {
  value: true,
});

module.exports = fixedSource;

[cblair]

I'm also seeing issues with this for jest 21.1.0 and babel-jest 21.0.2, the solution of disableAutomock and unmock have no effect:

index.test.js

jest.disableAutomock();
jest.unmock('ui');
import {Button} from 'ui';

node_modules/ui/index.js

export {default as Icon} from './icons/components/icon';

./node_modules/jest/bin/jest.js ./index.test.js

 FAIL  index.test.js
  ● Test suite failed to run

    TypeError: Cannot redefine property: Icon
        at Function.defineProperty (native)

      at Object.<anonymous> (node_modules/ui/index.js:4:198)
      at Object.<anonymous> (index.test.js:13:187)
      at next (native)
      at next (native)
      at process._tickCallback (internal/process/next_tick.js:103:7)

[cblair]

Looks like some are still having issues with this like, do we want to re-open this issue or create a new one? I'll try to help and submit a solution.

[stolinski]

I'm still having these errors. Has there been a fix?

[cblair]

The latest versions of babel-jest and... everything else worked for me. Try bumping versions, I’ll try to give you definite versions when I get back in.

[le0nik]

The issue still exists.
Ideally this should be reopened.

[SimenB]

@le0nik mind opening up a new issue with a reproduction?

[denissb]

I am also still facing the issue, I guess this needs to be reopened.

[SimenB]

No it doesn't, you're encountering a separate issue. The issue in the OP does not reproduce anymore. Please create a new issue including a reproduction

[denissb]

You are right, I was thinking that this issue is the cause while in the end I just had a recursive re-export. Probably many people still complaining on this issue have had the same problem.
These things are really difficult to debug in Jest and I wonder if anything can be done about that, maybe a feature request is in order.