Support for graceful extension of Jest config

[jamesmfriedman]

This PR fixes what I believe to be a very necessary fix for Jest configuration. #6042

What it does

• It adds 3 new keys to the allowedOverrides config
• It gracefully extends any jest config option that is an object while leaving arrays and primitive types to override
• Gracefully extending the objects made the most sense because it allows the original pieces to keep working as expected while give you the ability to fix things that would render the test framework useless for a project

We need to be able to update these keys for the following reasons

• moduleNameMapper: I've worked on many many jobs and projects and have yet to find one that didn't take advantage of aliasing in someway. If a project is using aliasing (despite CRAs efforts to continue to block it?) it renders the test framework useless.
• transform: adding any additional file types or loaders to a project will render this broken. Specifically here, I know people need to use jest-transform-graphql
• transformIgnorePatterns: This is really the reason this PR was created in the first place, the above two items were just logical additions... If someone distributes ES6 / ESNext code and you are using it in your project, you can no longer use Jest. While we can promote in a perfect world that everyone ships ES5 code, first class browser support for ES6 is making this less true. Also, some codebases intentionally use ES6 code since it results in smaller end user bundles. Lastly, The dev / build system supports this while Jest does not!

My current Jest key in package.json

Config before change, lacking my additions

Config after this PR :)

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[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[jamesmfriedman]

I had an open issue with that seemed to indicate this would be an ok addition. Something preventing it from being approved?

#6042

[jamesmfriedman]

Any word on this?

[jamesmfriedman]

Any word on this?

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[stale]

This pull request has been automatically closed because it has not had any recent activity. If you have a question or comment, please open a new issue. Thank you for your contribution!

[jamesmfriedman]

What the heck? This was a fix for an issue where a contributor said to do it.

[jamesmfriedman]

Thanks!

[petetnt]

Hi @jamesmfriedman,

first of all, sorry for the late response.

I'd revert the other changes than those in createJestConfig.js ( merge issues? or is GH UI just fooling me). Also these additional keys need to be documented in https://facebook.github.io/create-react-app/docs/running-tests#configuration

Otherwise I am a-okay with the idea itself

Thanks!

[jamesmfriedman]

Yeah weird, those all popped in after I rebased 🙄. I’ll just port the changes over to the latest master and force push over this branch.

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[jamesmfriedman]

@petetnt took me a while to remembe to get back to this, fixed my PR as requested ^

[jamesmfriedman]

Commenting so it doesn't got stale again

[mrmckeb]

This is great, thanks @jamesmfriedman.

Would you mind adding a PR to document this?

[jamesmfriedman]

Glad this finally made it in! Yeah sure thing. Haven’t looked since the new docs site went live but I’m assuming the src is in the repo? I’ll assume yes unless you tell me otherwise.

[mrmckeb]

That's correct @jamesmfriedman