Error message when comparing Immutable-js collection to array is confusing

[Daniel15]

Do you want to request a feature or report a bug?
Enhancement request (so feature, I guess?)

What is the current behavior?
Given a test like this:

const Immutable = require('immutable');
it('compares Immutable-js collections', () => {
  expect(Immutable.OrderedSet(['foo'])).toEqual(['foo']);
});

The failure message is a bit confusing:

 FAIL  html/js/ads/utils/__tests__/SomeTest-test.js
  â— compares Immutable-js collections

    expect(received).toEqual(expected)

    Expected value to equal:
      ["foo"]
    Received:
      ["foo"]

    Difference:

    Comparing two different types of values:
      Expected: array
      Received: object

      at Object.<anonymous> (html/js/ads/utils/__tests__/SomeTest-test.js:38:50)
      at process._tickCallback (internal/process/next_tick.js:103:7)

What is the expected behavior?
Maybe something like this:

    Comparing two different types of values:
      Expected: array
      Received: Immutable.OrderedSet

Or this:

    Expected value to equal:
      ["foo"]
    Received:
      Immutable.OrderedSet("foo")

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.
Whichever version of Jest we use internally at Facebook.

[thymikee]

We could definitely create a pretty-format plugin for that

[ttmarek]

@thymikee I can give this a shot if no one else will. I'd like to contribute more to the Jest ecosystem...and this seems like a small enough issue to start off with. I might even have some time this weekend. Any tips on where to start are welcome 🙂

[thymikee]

@ttmarek great! Of course you can take it.

For the Jest part you can start with looking at how to write a plugin for pretty-format package and how to detect that the value passed to it is coming from Immutable library.
Then you'll need to update prettyFormat calls with plugins option in Jest codebase.

[cpojer]

This will be in the next version of Jest thanks to @cpenarrieta.

[github-actions]

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