Babel 7.4 + core-js 3 causing tons of padded zeros in Jest tests

Bug Report

Current Behavior

I’m in the process of upgrading an internal project to Babel 7.4 (from 7.2) and core-js 3 (from 2). The Webpack bundle works fine, however, a ton of Jest tests are failing with unexpected values being padded with a ton of zeros. Some examples:

<Rating /> › renders the star rating

    expect(received).toBe(expected) // Object.is equality

    Expected: "12"
    Received: "00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"

 <Row /> › renders data

    expect(received).toBe(expected) // Object.is equality

    Expected: "7"
    Received: "0000000000000000000000000000000000000000000000000000000000000000"

<BottomBar /> › renders the correct content for end steps

    expect(value).toMatchSnapshot()

    Received value does not match stored snapshot "<BottomBar /> renders the correct content for end steps 1".

    - Snapshot
    + Received

    @@ -5,13 +5,43 @@
          className="primary_4ommi7"
        >
          <Text
            muted={true}
          >
    -       5
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
             / 
    -       5
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
    +       0
          </Text>
        </div>
        <div
          className="after_m2rwu8"
        >

I’ve tried all the following combinations. Seems anything using core-js v3 is broken.

• Babel 7.4 + core-js 2 - WORKS
• Babel 7.4 + core-js 2 + “usage” built-in - WORKS (but logs warnings)
• Babel 7.4 + core-js 3 + “usage” built-in - FAILS with padded zeros
• Babel 7.4 + core-js 3 + “entry” built-in - FAILS with padded zeros

Input Code

Internal only but it’s just basic React components.

Expected behavior/code

It simply works with core-js 3.

Babel Configuration (.babelrc, package.json, cli command)

const isTesting = process.env.NODE_ENV === 'test';

module.exports = {
  presets: [
    [
      '@babel/preset-env',
      {
        // corejs: 3,
        // useBuiltIns: 'usage',
        loose: true,
        shippedProposals: true,
        targets: isTesting ? { node: 'current' } : { browsers: ['last 3 Chrome versions'] },
        modules: isTesting ? 'commonjs' : false,
      },
    ],
    '@babel/preset-react',
    '@babel/preset-typescript',
  ],
  plugins: [
    'babel-plugin-graphql-tag',
    // TS doesn't support optional chaining, so we use idx instead
    'babel-plugin-idx',
    '@babel/plugin-proposal-class-properties',
    [
      '@babel/transform-runtime',
      {
        // corejs: 3,
        helpers: true,
        regenerator: false,
        useESModules: !isTesting,
      },
    ],
    'react-loadable/babel',
  ],
};

Environment

• Babel version(s): 7.4.3
• Node/npm version: node 10.14 / npm 6.5 / yarn 1.15
• OS: OSX 10.14
• Monorepo: no
• How you are using Babel: cli

Possible Solution

Digging into root cause. Found nothing yet.

Additional context/Screenshots

N/A

[milesj]

@nicolo-ribaudo Honestly, never figured this out. I ended up deleting the lock file, updating all versions to the latest, and just migrating everything. It eventually went away, so I’ll close this.

Seems like it was a weird combo of certain dep versions.

[nicolo-ribaudo]

Hi @milesj, sorry for the long delay. Would you be able to create a repository I can download to reproduce the issue? I have never used enzyme, so I don’t know where to start from.