test: add toWarnDev custom Jest matcher

[francoischalifour]

This adds a custom Jest matcher to assert that warnings are reported correctly in development mode. This matcher is called toWarnDev and is inspired by the one developed by the React team.

It was quite cumbersome to assert that connector/widget warnings were reported and led us to sometimes skip these checks.

This PR aims at reducing this friction and providing a tool to improve DX.

Before

test('with `hidden` as boolean warns', () => {
  const warn = jest.spyOn(global.console, 'warn');
  warn.mockImplementation(() => {});

  panel({
    hidden: true,
  });

  expect(warn).toHaveBeenCalledWith(
    '[InstantSearch.js]: The `hidden` option in the "panel" widget expects...'
  );

  warn.mockRestore();
});

After

Usage

test('with `hidden` as boolean warns', () => {
  expect(() => {
    panel({
      hidden: true,
    });
  }).toWarnDev(
    '[InstantSearch.js]: The `hidden` option in the "panel" widget expects...'
  );
});

Output

[algobot]

Deploy preview for instantsearchjs ready!

Built with commit dbb5d33

https://deploy-preview-3574--instantsearchjs.netlify.com

[Haroenv]

Would be amazing if it could be an inline snapshot. Is that possible?

[francoischalifour]

That would be a lot more difficult because inline snapshots rely on Prettier, file system and custom parsers.

You can learn more in the original inline snapshots thread and in the Jest source code.

I'm not aware of any helper for that.

I would suggest sticking with regular expectations.

[tkrugg]

looks good and DRYer indeed!