Snapshot testing

[mattphillips]

Question/Feature request.

Hey I'm noticing issues with Snapshots ran on differing operating systems (see #6102 and #6113 as examples).

Is it possible to specify the percentage a snapshot should match on? For example match 90% of the snapshot, allowing for 10% error rate which we don't care about.

If not, and this is something people don't want to add, perhaps a new matcher should be created to deal with whitespace, tabs and newlines etc.

test('ignores whitespace etc', () => {
  expect(`\t hello world\n

                    foo
bar
baz
`).toMatchSnapshotIgnoringXXX();
});
↓↓↓ snapshot ↓↓↓

exports[`ignores whitespace etc 1`] = `
"	 hello world


                      foo
  bar
  baz
  "
`;

This snapshot could be stored with the whitespace etc to keep it human readable but when compared to the value both could be normalised.

[rickhanlonii]

@mattphillips would this be solved by #5847?

With that you could do:

test('ignores whitespace etc', () => {
  expect(`\t hello world\n

                    foo
bar
baz
`).toMatchSnapshot(
  expect.stringMatching(/hello world/),
);

Another option we've discussed - exposing toMatchSnapshot to custom matchers so you could do something like:

expect.extend({
  toMatchSnapshotTrimmed: (received) => {
    return this.toMatchSnapshot(received.trim());
  }
})

[mattphillips]

@rickhanlonii #5847 looks very cool and would certainly help with this! Whats happening with the proposal is it currently being worked on?

I think exposing toMatchSnapshot to custom matchers would be slick too, then we could create matchers like toMatchSnapshotTrimmed in jest-extended is any work happening on this too?

[SimenB]

@mattphillips mind changing this issue (or opening up a new one) to be about exposing toMatchSnapshot to custom matchers?

[mattphillips]

Closed in favour of #6144

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