Messages from custom AssymetricMatchers are ignored

[jayarjo]

🐛 Bug Report

Messages from custom AssymetricMatchers are ignored, while according to the following illustration, they were meant to be taken into account.

To Reproduce

Simply try to run the example from illustration, but force it to fail (the one above succeeds so no error messages have to be shown):

expect.extend({
    toBeDivisibleBy(actual, expected) {
        const pass = actual % expected === 0;
        const message = pass
            ? () => `expected ${actual} not to be divisible by ${expected}`
            : () => `expected ${actual} to be divisible by ${expected}`

        return { message, pass }
    }
})

test("example asymetric matchers", () => {
    expect({ value: 3 }).toEqual({ value: expect.toBeDivisibleBy(2) })
})

Expected behavior

As illustration shows, one would expect a proper error message to be displayed.

Run npx envinfo --preset jest

Paste the results here:

$ npx envinfo --preset jest
npx: installed 1 in 2.228s

  System:
    OS: Windows 10
    CPU: (4) x64 Intel(R) Core(TM) i7-6560U CPU @ 2.20GHz
  Binaries:
    Node: 10.11.0 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.9.4 - ...\YARN\BIN\yarn.CMD
    npm: 6.4.1 - ...\nodejs\npm.CMD

[rickhanlonii]

@jayarjo thanks to submitting

I ran the above code and I see the expected failure:

[jayarjo]

Is this expected? Looks more like generic default. What about expected ${actual} not to be divisible by ${expected} part?

In my case AssymetricMatcher is matching two URLs and I was looking for a way to output detailed information about what parts of the URLs actually differ. Query string especially, since the order of the fields can be arbitrary and also I wanted to have a partial matcher (when one query string contains another, but is not exactly equivalent).

[rickhanlonii]

Yeah this is expected, the matcher is toEqual so we show it's error message

Here's what toBeDivisible outputs when called as a matcher:

In the original case, it's being called as a asymmetric matcher so we only use the pass/fail indicator when comparing equality and don't use the message

[jayarjo]

:/

But won't it be a great feature, if nested asymmetric matchers would be able to show full messages? In the case above matcher is trivial, so it's self-explanatory even with generic message what exactly went wrong. Potentially they might be (and actually are more useful if they are) much more complex than that. Take objectContaining for example - at the moment it is not able to show exactly what props didn't match, it just spits out whole stringified object and then one has to look up the diff in the wrapped lines (sometimes huge) manually.

[rickhanlonii]

Yes, we could definitely improve here, just closed this because it's not a bug

Would you be interested in submitting a feature proposal with a suggestion on how we could improve common use cases?

[SimenB]

Heh, sorry about the churn...

[github-actions]

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