Jest: [New matcher request] toHaveBeenCalled{Last}MatchingSnapshot

[SimenB]

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
The matcher doesn't exist. 😭

The current snapshot testing is amazing, but I'd also like to be able to use it for checking stubs without going through extracting .mock.calls etc.

I started on a patch for this, but if you don't want the feature I don't want to waste time on it. If you _do_ want it, I can provide a PR for it. 😄

[thymikee]

whoa this is a long name for a function!

[SimenB]

Is that a :-1: or :+1:? :grinning:

[thymikee]

Frankly I don't know, but I personally don't like such long names. Could you please provide a sample usage? It would be easier to think about this.

[SimenB]

The name itself was just to match the existing ones, I'm sure it can be shortened 😄

Usage sample:

test('some component', () => {
  const someObject = { method: jest.fn() };

  someFunction(someObject);

  expect(someObject.method).toHaveBeenCalledWith({
    prop: 'foo',
    prop2: 'bar',
    baz: 'foobar',
  }, true);

  // or, if I know which invocation
  expect(someObject.method.mock.calls[0]).toMatchSnapshot();

  // or, if this feature is implemented
  expect(someObject.method).toHaveBeenCalledMatchingSnapshot();
});

The middle one is OK, but I have to extract the correct call if there are multiple. or just do expect(someObject.method.mock.calls).toMatchSnapshot();, but then I assert on every single call. Might be fine, though? Reaching into the mock object feels kinda dirty though, even though it's public API.

[bookman25]

As an alternative to:
toHaveBeenCalledWith(jasmine.objectContaining({}))

We wrote the following extension:

toBeCalledWithSnapshot(received) {
  return require('jest-snapshot').toMatchSnapshot.call(this, received.mock.calls);
}

[cpojer]

I don't think this is something we'd like to support inside of Jest directly at this point. Maybe you can build a snapshot extension library using expect.extend? :)

[SimenB]

Will do! Thanks

[rattrayalex]

@SimenB Would you mind providing a copy-pastable snippet or a link to a library?

(Seems fairly easy to piece together, but always nice to have something packaged if it's convenient for you).

[SimenB]

We've made a serializer for mocks in the next version of Jest, so just do expect(myMock).toMatchSnapshot().

See this for examples on how it looks: https://github.com/facebook/jest/blob/4883838c16471fd3447c5fea1ab261140d37f7c6/packages/jest-snapshot/src/__tests__/__snapshots__/mock_serializer.test.js.snap

Available in jest@test (release coming soonish - #4948)

[rattrayalex]

Awesome!

[kirillgroshkov]

great thread! I've found what I wanted! expect(myMock).toMatchSnapshot()