Support async/await in jest tests

[thektan]

When using async/await in tests the following error is thrown:

ReferenceError: regeneratorRuntime is not defined

Possible Solutions

Option 1

According to Jest docs:

To enable async/await in your project, install @babel/preset-env and enable the feature in your babel.config.js file.

In .babelrc

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "targets": {
          "node": "current"
        }
      }
    ]
  ]
}

(Sources: jestjs/jest#3126 (comment), babel/babel#7601 (comment))

Option 2

Installing @babel/plugin-transform-runtime and adding the following configuration to .babelrc

{
  "env": {
    "test": {
      "plugins": ["@babel/plugin-transform-runtime"]
    }
  }
}

(Sources: jestjs/jest#3126 (comment), babel/babel#8829 (comment))

Option 3

Importing babel-polyfill to the jest setup.js file. Which would mean adding babel-polyfill as a new devDependency.

import 'babel-polyfill';

(Source: babel/babel#5085 (comment))

Final Comments

I'm currently using Option 2 since it scopes the plugin to just the tests (where the issue is only occurring), but I'd like to hear everyone else's opinion since I haven't noticed any differences with any of these fixes besides Option 3 throwing a new error Warning: Can't perform a React state update on an unmounted component in the tests (but that's probably something I'd need to fix in the component/tests itself).

[wincent]

Given that we currently use Node v10.15.1 in liferay-portal (which has native async/await support), it would be nice to see how far we can get with "Option 1", because it means Babel will skip some of the heavier-weight transforms that it does (including relying on the regenerator runtime) — I think we should be able to apply this for the test environment only.

[thektan]

@wincent It looks like we could do something like this example from the jest docs:

Jest will set process.env.NODE_ENV to 'test' if it's not set to something else. You can use that in your configuration to conditionally setup only the compilation needed for Jest, e.g.

// babel.config.js
module.exports = api => {
  const isTest = api.env('test');
  // You can use isTest to determine what presets and plugins to use.

  return {
    // ...
  };
};

We also might need to add jest-babel and @babel/core? The docs also say:

To use Babel, install required dependencies via yarn:

yarn add --dev babel-jest @babel/core @babel/preset-env

[wincent]

Closing this because I am about to cut a release, so this will go to liferay-portal master today (at least, I'll submit the PR today).