If the received is different from the expected in some obvious way, reject it without full diff

[cmdcolin]

🚀 Feature Proposal

Create a way to reject the test without a full diff?

Motivation

This report comes from a instance where I had a unserialized class object with some internal data that I compared to serialized JSON (the expected) and the output was giving memory errors. I should have been serializing the classes themselves but when I forgot to do so I questioned my sanity and the code because of these memory errors and jest never terminating

Example

This code produces the "bug" but since this sort of thing is potentially outside of the scope of bugs I am filing it as feature request
https://github.com/cmdcolin/jest_neverfinish

My only proposal is that somehow this would be "caught" without running forever or producing memory errors but potentially this is misguided

Pitch

If this feature was added to clearly reject something by partially diffing, then it would save headaches that make you think your actual code is faulty instead of the test being faulty!

[cmdcolin]

I actually did not dig into it to see where the exact reason for the long running is but I figured it was diffing, hence my suggestion for partial diffing. I'd be curious also why this instance just takes a long time in general if it is an issue with the diffing?

[pedrottimark]

@cmdcolin Thank you for link to repo!

With local version of pending improvement #6961, jest-diff call runs in 14 seconds on node 8.12.0

The size of diff output is 6266344

The test still fails for reason that will take some more time to investigate:

 ● Test suite failed to run

    RangeError: Maximum call stack size exceeded
        at RegExp.[Symbol.match] (<anonymous>)
        at String.match (native)

      at exports.separateMessageFromStack.content (node_modules/jest-message-util/build/index.js:368:32)
          at Array.map (<anonymous>)

[cmdcolin]

Interesting, thanks for taking a look at it and I'm definitely interested to see how this new diff performs. I was basically unsure whether my request was within the scope of jest but it's great to see that there might be some solutions :)

[pedrottimark]

Interesting, with or without improvement to diff-sequences package, the test fails successfully if I replace fs.readFileSync('test.txt') with fs.readFileSync('test.txt', 'utf8')

That is, whether pretty-format package serializes a file buffer (as array of integers) versus a multiline text string. That has come up before. This might make a good minimal reproduction.

@cmdcolin Without revealing proprietary details, does internal data of your class include a buffer?

[cmdcolin]

Indeed it did include buffers and that was particularly why I reproduced it in the test

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