Jest tests hanging forever with large snapshot changes

[digitalsadhu]

Jest tests hanging forever when there have been large snapshot changes. Running jest -u seems to fix the issue.

Reproduce by pulling down this branch and running jest. It should sit spinning forever. Run jest -u to fix. Subsequent calls to jest should work.

[SimenB]

/cc @pedrottimark could you take a look at this? My guess is that the diff generation ends up in some sort of loop, preventing both the diff from being generated, and the test from timing out.

[pedrottimark]

@SimenB @digitalsadhu Yes, this looks like same problem #1772 which I have been working on.

Very timely to have more offline stress tests. I will put received and expected serializations into separate files to measure heap used by improved diff-sequences versus baseline diff package.

[pedrottimark]

@digitalsadhu Unrelated to the problem, is there a duplicated assertion in reader.test.js under the last test 'bundling dedupes common modules' what a delightful pun :)

https://github.com/asset-pipe/asset-pipe-js-reader/blob/jest_large_snapshots_run_forever/test/reader.test.js#L287-L290

[pedrottimark]

And the winner is should concat 2 files snapshot diff on node 9.4.0:

package	heap used	elapsed time
diff-snapshot	12,088,376	0.040633
diff	169,757,848	295.061440

Unlike previous example from React, this example has similar number of expected and received lines and a smaller (almost a quarter though) proportion of changed lines:

category	lines
expected	35,132
received	27,823
common	27,805
delete	7,318
insert	18

[SimenB]

Thanks for digging in!

Are you saying this is a duplicate of #1772, and can be tracked there? Is there anything we can do currently to at least be able to time out the test? Or should we just wait until the underlying issue is fixed?

[digitalsadhu]

@pedrottimark hah! right you are. Very punny. ;)

[pedrottimark]

@SimenB We can let this shorter issue be primary and the earlier longer issue be secondary.

1. I will open a pull request for new package today or tomorrow. Besser spät als nie :)
2. As soon as that is reviewed and merged, I will convert jest-diff to [EDIT: call the] new package.
3. And then, I can open a replacement for dormant pull request to diff substrings.

[sumanthns]

Hi @pedrottimark , We are also facing the same issue. Are there any updates? Did you get a chance to open a pull request?

[SimenB]

#6961