Default to React Native Jest Preprocessor

🚀 Feature Proposal

If using the react-native preset, the transformer should default to the react-native/jest/preprocessor.js. If left off, it doesn’t transform anything. And React Native defaults to its own transformer so adding an extra babel.config.js just for tests seems redundant when all the pieces are already there.

Motivation

One less package (metro-jest-babel-resolver or something like that) and one less config file for default RN projects (babel.config.js)

Example

The only thing you need to get a simple RN project up and running in Jest should be:

{
  preset: "react-native"
}

Currently, you need this extra line:

    "preset": "react-native",
    "transform": {
      "\\.(js|ts|tsx)$": "./node_modules/react-native/jest/preprocessor.js"
    },

Pitch

Makes the requirements to use Jest for React Native even smaller and more concise.

[SimenB]

Should be fixed now: #10910

[SimenB]

You need to build jest first. Run yarn build:js in root, then you should be able to run the example.

This is covered by the contribution guide, fwiw