Jest: The mock mecanism does not support omiting the `.json` when requiring a file

[Spy-Seth]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
Jest fail to mock a dependency and throw an error

$ jest tests/units/WebsiteBuilding/Infra/HttpTranslationMessageRepositoryTest.js
 FAIL  tests/units/WebsiteBuilding/Infra/HttpTranslationMessageRepositoryTest.js
  ● Test suite failed to run

    Cannot find module './package' from 'index.js'

      at Resolver.resolveModule (node_modules/jest-resolve/build/index.js:160:17)
      at Object.<anonymous> (node_modules/got/index.js:19:13)

Adding the .json suffix manually in the node_modules/got/index.js file resolve the issue.

What is the expected behavior?
Jest should detect that the file referenced by ./package is a JSON file and work correctly with it. Omitting the extension when requiring a json file is a valid usage of the require function:

LOAD_AS_FILE(X)
1. If X is a file, load X as JavaScript text.  STOP
2. If X.js is a file, load X.js as JavaScript text.  STOP
3. If X.json is a file, parse X.json to a JavaScript Object.  STOP
4. If X.node is a file, load X.node as binary addon.  STOP

https://nodejs.org/api/modules.html#modules_all_together

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.

Reproduced on jest v19.0.0 and v19.0.1.
Node v7.6.0

[cpojer]

Can you provide a repro?

[Spy-Seth]

I'm trying to reproduce the behavior in a simple repository but I do not succeed. Maybe it's link to a more complex environment parameter that I do not succeed to reproduce.

[Spy-Seth]

I just notice that event if do not mock the module the error is throw

[cpojer]

Ok, I think this is not a Jest issue. Feel free to ask more on the Jest discord channel and respond here if you can create a repro so if there is a bug in Jest we can fix it.

[Spy-Seth]

I find the source of the issue!

In my jest config I have set these extensions: "moduleFileExtensions": [ "js", "jsx" ],.
If I add the json extension here "moduleFileExtensions": [ "js", "jsx", "json" ], the error is fixed!

It seems that's a pretty dangerous side effect! I think that the js and json extension should be always activated as there are part of the default behavior. The dependencies of a project will relies on this behavior.

The source of this behavior are in the jest-resolve package: https://github.com/facebook/jest/blob/master/packages/jest-resolve/src/index.js#L91