Don't include unref'd timers in --detectOpenHandles results

[pimterry]

Fix #8939

Note that this shouldn't affect any behaviour in Node < 11, and because of that the test is skipped in older versions. It passes happily for me locally with Node 12.9.1 though.

It would be possible to extend this to cover old versions later on (by wrapping ref()/unref()) if that seems worthwhile for somebody.

[codecov-io]

Codecov Report

Merging #8941 into master will decrease coverage by 0.05%.
The diff coverage is 6.66%.

@@            Coverage Diff             @@
##           master    #8941      +/-   ##
==========================================
- Coverage   64.23%   64.18%   -0.06%     
==========================================
  Files         276      276              
  Lines       11700    11712      +12     
  Branches     2864     2867       +3     
==========================================
+ Hits         7516     7517       +1     
- Misses       3552     3563      +11     
  Partials      632      632

Impacted Files	Coverage Δ
packages/test-utils/src/ConditionalTest.ts	0% <0%> (ø)	⬆️
packages/jest-core/src/collectHandles.ts	2.08% <9.09%> (+2.08%)	⬆️

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[jeysal]

Awesome, thanks a lot @pimterry!
I've verified locally that the test fails with collectHandles.ts@master

[SimenB]

This is great, thanks for tackling it! I didn't know about hasRef

[pimterry]

Now updated with some more general conditional testing logic.

I couldn't quite follow the existing pattern (.only seems to disable all the other tests in the file, regardless of describe), but I've added some conditional logic that gives the same effect, showing the tests in the output as explicitly skipped.

In Node 10:

 PASS  e2e/__tests__/detectOpenHandles.ts (5.171s)
  ✓ prints message about flag on slow tests (1779ms)
  ✓ prints message about flag on forceExit (750ms)
  ✓ prints out info about open handlers (706ms)
  ✓ does not report promises (726ms)
  ✓ prints out info about open handlers from inside tests (711ms)
  [SKIP] tests that require node >=11
    ○ skipped does not report timeouts using unref

Test Suites: 1 passed, 1 total
Tests:       1 skipped, 5 passed, 6 total
Snapshots:   4 passed, 4 total
Time:        5.201s

In Node 12 the [SKIP] wrapper doesn't appear, and it runs like any other test:

 PASS  e2e/__tests__/detectOpenHandles.ts (5.241s)
  ✓ prints message about flag on slow tests (1655ms)
  ✓ prints message about flag on forceExit (704ms)
  ✓ prints out info about open handlers (621ms)
  ✓ does not report promises (642ms)
  ✓ does not report timeouts using unref (638ms)
  ✓ prints out info about open handlers from inside tests (642ms)

Test Suites: 1 passed, 1 total
Tests:       6 passed, 6 total
Snapshots:   4 passed, 4 total
Time:        5.268s, estimated 6s

[SimenB]

Barring lint (prettier) errors reported by CI, this LGTM. Super awesome contribution, thank you!

[github-actions]

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