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The commit message "Fix mozilla expectations after regexp change" looked interesting to me and I took a look at the change.

https://chromium.googlesource.com/v8/v8.git/+/5d65e1374fd9c5...

Looks like V8 runs Mozilla's JS tests too. I didn't know that. Does Mozilla do something similar to ensure that V8's tests work in Mozilla(Firefox) as well?

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Mozilla's JS tests have for a while been run by everyone else because they have typically tested a lot of de-facto required behaviour that isn't specified anywhere. That said, the problem with both them and mjsunit (V8's JS testsuite) is they freely mix tests for unimportant implementation detail (say, details of enumeration order!) and what is de-facto required. In the end, with Carakan, we decided it wasn't worth the time to get the mjsunit tests running — they found almost nothing that weren't found otherwise — and coming up with proper expectations and keeping them up to date does take time.

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