Unintended breaking change in snapshot tests in jest 23?

[robin-drexler]

💥 Regression Report

I've upgraded to jest 23 and found the following behavior change when it comes to undefined props in snapshots.

Last working version

v22.4.4
Worked up to version:
v22.4.4

Stopped working in version:
v23

To Reproduce

Consider the following test:

import React from 'react';
import renderer from 'react-test-renderer';

const Foo = ({ href, target }) => <a href={href} target={target} />;

describe('<Foo />', () => {
  it('renders snapshot', () => {
    expect(
      renderer.create(<Foo href={'https://github.com/facebook/jest'} />)
    ).toMatchSnapshot();
  });
});

In jest 22 the resulting snapshot was:

// Jest Snapshot v1, https://goo.gl/fbAQLP

exports[`<Foo /> renders snapshot 1`] = `
<a
  href="https://github.com/facebook/jest"
  target={undefined}
/>
`;

Running the same test in jest 23 produces:

// Jest Snapshot v1, https://goo.gl/fbAQLP

exports[`<Foo /> renders snapshot 1`] = `
<a
  href="https://github.com/facebook/jest"
/>
`;

The target={undefined} has been removed, causing the test to fail.
I could not find anything related to that in the changelog. Is this an intended change

Expected behavior

Snapshots should look the same as in in jest 22

Run npx envinfo --preset jest

Paste the results here:

npx: installed 1 in 1.556s

  System:
    OS: macOS Sierra 10.12.5
    CPU: x64 Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz
  Binaries:
    Node: 9.3.0 - ~/.nvm/versions/node/v9.3.0/bin/node
    Yarn: 1.5.1 - ~/.yarn/bin/yarn
    npm: 6.0.1 - ~/.nvm/versions/node/v9.3.0/bin/npm
  npmPackages:
    jest: ^23.0.0 => 23.0.0

[SimenB]

It's called out in the changelog as a breaking change. Comes from #6162.

[robin-drexler]

ooops, overlooked that. Thank you!

[github-actions]

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