test(neo4j): give OptimisticLockingSpec's cross-thread heisenbug more headroom

[borinquenkid]

Summary

CI on #15972 (Neo4j GormRegistry migration) hit a failure in OptimisticLockingSpec > Test optimistic locking on a loaded macos-latest runner, consistently across all 3 matrix legs of that run.

Investigation (see discussion on #15972) traced this to the test's own pre-existing timing sensitivity, not a regression from the GormRegistry/Neo4jGormApiFactory wiring:

• The unmodified test passes locally, deterministically, against the exact commit that failed in CI — including correct OptimisticLockingException detection through the new registry-based API resolution.
• The background thread's write is already synchronized with the main thread via .join() before the sleep runs, so the sleep isn't providing thread-completion synchronization — it's headroom for the embedded Neo4j 3.5.x test harness's own write durability.
• The test's own code comment (// heisenbug) already flags this as a known flaky spot.

A loaded CI runner can apparently push that durability window past the existing 2-second sleep. This PR bumps it to 5 seconds in both affected examples (Test optimistic locking and Test optimistic locking disabled with 'version false') and documents why, rather than leaving the bare // heisenbug comment.

Test plan

• :grails-data-neo4j-core:test --tests "grails.gorm.tests.OptimisticLockingSpec" — 3 tests, 0 failures (verified against both this branch's file and PR Neo4j GormRegistry migration (consolidated: replaces #15816, #15951, #15817, #15832, #15833) #15972's copy of the same file, which is otherwise unchanged content, just relocated by that PR's module restructuring)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR aims to reduce CI flakiness in the Neo4j GORM test suite by giving the known timing-sensitive OptimisticLockingSpec tests more durability headroom on loaded runners, and documenting the rationale for the wait.

Changes:

• Increased the post-join sleep in two optimistic-locking-related tests from 2s to 5s.
• Replaced the vague // heisenbug note with a clearer explanation of what the delay is intended to cover.

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[bito-code-review]

The suggestion to replace sleep with a bounded join() is technically sound and improves test reliability. Using thread.join(timeout) combined with an assertion that the thread has actually finished (e.g., assert thread.isAlive() == false) ensures the test waits for the thread to complete rather than relying on an arbitrary sleep duration, which is prone to race conditions in loaded environments.

grails-data-neo4j/grails-datastore-gorm-neo4j/src/test/groovy/grails/gorm/tests/OptimisticLockingSpec.groovy

def t = Thread.start { ... }
        t.join(5000)
        assert !t.isAlive()

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.1558%. Comparing base (e049502) to head (184020c).
⚠️ Report is 1 commits behind head on feat/gorm-registry-core-impl.

Additional details and impacted files

@@                          Coverage Diff                           @@
##             feat/gorm-registry-core-impl     #16070        +/-   ##
======================================================================
- Coverage                         52.1714%   52.1558%   -0.0155%     
+ Complexity                          18415      18408         -7     
======================================================================
  Files                                2054       2054                
  Lines                               96622      96622                
  Branches                            16846      16846                
======================================================================
- Hits                                50409      50394        -15     
- Misses                              38823      38835        +12     
- Partials                             7390       7393         +3     

see 3 files with indirect coverage changes

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