Jest: Add the ability to specify modules to reset in jest.resetModules

[benmj]

🚀 Feature Proposal

Allow passing variable arguments to jest.resetModules to specify which modules should be reset.

Motivation

I have several files that contain local state which I would like to reset between tests. However, I do not want to reset and re-import all of the dependencies in the test file because this seems 1) unnecessary and 2) error prone and easy to forget.

Example

Current

Here is a somewhat simplified example:

jest.mock('logger');

let logger;
let myModule;

beforeEach(() => {
    jest.clearAllMocks()
        .resetModules();

    logger = require('logger');
    myModule = require('../myModule');
});

Desired

jest.mock('logger');
const logger = require('logger');

let myModule;

beforeEach(() => {
    jest.clearAllMocks()
        .resetModules('../myModule'); // pass in the desired file to be reset

    /** only reload the module that I want to reset **/
    myModule = require('../myModule');
});

Pitch

It would remove cruft, add specificity, and give finer-grained control.

[thymikee]

How about filling issue template?

[rogeliog]

Hi, thanks for reporting!

This seems like an interesting use case. Here is the code for resetModules. https://github.com/facebook/jest/blob/master/packages/jest-runtime/src/index.js#L421-L441

My initial impression is that if we want to support this, it would not be that hard, except for a couple of things:

• By resetting one module, do we need to invalidate any other parts of the module registry? My guess is that we shouldn't need to.
• What should be the expected behavior for this._environment.global and envGlobal.mockClearTimers when "module path" arguments are passed?

Given that resetModules has remained untouched for 2+ years, https://github.com/facebook/jest/blame/master/packages/jest-runtime/src/index.js#L421-L441, I guess @cpojer might have better insights.

[rogeliog]

@benmj I understand the use case for just resetting one module rather than all of them. I'm trying to reproduce and better understand the implications of:

I also need to re-require other modules that do not contain local state.

Do you mind providing an example?

Is this similar to what you are mentioning?

import x from './withLocalState';
import y from './stateless';

beforeEach(() => {
  jest.resetModules();
});

it('some test', () => {
   // In here `y` is still the correct object right?
})

[rickhanlonii]

@benmj our Feature Proposal template should be followed for all feature proposals. It has sections for questions that will come up like the ones @rogeliog brings up

I think this is a great proposal, so let us know when you update the description to follow that template and we'll reopen

[SimenB]

Would #6174 fulfill the use case?

[benmj]

Thanks for the comments. I've updated to follow the template.

[rickhanlonii]

Thanks for the update 👍

[rogeliog]

I agree with @SimenB about @gaearon's proposal(#6174). Even though it uses a different abstraction, would it be correct to say that both proposals are trying to solve a same or a similar problem?

[rogeliog]

Closing in favor of #6174