Proposal: toMatchSnapshot property matchers

[rickhanlonii]

Motivation

Objects often contain variable data. Unfortunately, the current snapshot API requires "cleaning" these values out of the object before passing to toMatchSnapshot. This proposal is to give users the ability to specify the shape of the object in the snapshot.

Proposal

I propose that toMatchSnapshot accepts a new argument which is deeply merged into the received object before snapshotting. If the value of the merge object field is an asymmetric matcher, the matcher is verified and then the name of the matcher is used in the snapshot.

Example

const user = {
  id: 'user-id',
  rev: 3, // increments on save
  createdAt: 1521639165339,
};

test('user', () => {
  expect(user).toMatchSnapshot({
    rev: 1,
    createdAt: expect.any(Date), 
  })
});

// snapshot
exports[`user 1`] = `
Object {
  "createdAt": '[expect.any(Date)]',
  "id": "user-id",
  "rev": "1",
}
`;

Why core

This could be solved with a custom matcher. I think this should be in core because:

• It neatly ties together snapshots and asymmetric matchers (main reason)
• Improves experience for API snapshot testing (many APIs return dates), inviting non-web devs
• Core currently has all of the control for snapshots and does not expose it to custom matchers

[github-actions]

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