Implement IsTestThread to fix flaky TestFlushExceptions - #1382
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LuceneTestCase.IsTestThread was hardcoded to always return true, so the flush-failure injection in TestConcurrentMergeScheduler.TestFlushExceptions fired on background ConcurrentMergeScheduler merge threads (which also flush via CompressingStoredFieldsWriter.Flush()), not just the test thread. When a merge thread happened to be flushing during the SetDoFail()/Flush() window and Random.NextBoolean() returned true, the merge threw, surfacing as a flaky MergeException at teardown. Capture the test-case thread in SetUp() (cleared in TearDown()) in a [ThreadStatic] field and have IsTestThread compare against it, mirroring Java's ThreadAndTestNameRule.testCaseThread. Tests run with LevelOfParallelism(1), and NUnit's TimeoutCommand (active via the assembly-wide [Timeout]) runs SetUp, the test body, and TearDown on the same thread, so the capture lines up with the thread executing the test method. Background merge threads never run SetUp, so they correctly see a null test thread and are excluded. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Pull request overview
This PR fixes a long-standing test-framework issue where LuceneTestCase.IsTestThread always returned true, which allowed failure injection in TestConcurrentMergeScheduler.TestFlushExceptions to fire on background merge threads and cause flaky MergeException failures.
Changes:
- Capture the current test-case thread during
LuceneTestCase.SetUp(). - Clear the captured thread during
LuceneTestCase.TearDown()(in afinallyblock). - Implement
IsTestThreadto returntrueonly for the captured test thread.
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NightOwl888
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Jun 23, 2026
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Approved with optional additional support.
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Implement IsTestThread to fix flaky TestFlushExceptions
(Related to flaky failure on #1311 / #1284)
Description
LuceneTestCase.IsTestThreadwas hardcoded to always return true, so the flush-failure injection inTestConcurrentMergeScheduler.TestFlushExceptionsfired on background ConcurrentMergeScheduler merge threads (which also flush viaCompressingStoredFieldsWriter.Flush()), not just the test thread. When a merge thread happened to be flushing during the SetDoFail/Flush window andRandom.NextBoolean()returned true, the merge threw, surfacing as a flaky MergeException at teardown.Capture the test-case thread in SetUp (cleared in TearDown) in a
[ThreadStatic]field and have IsTestThread compare against it, mirroring Java'sThreadAndTestNameRule.testCaseThread. Tests run withLevelOfParallelism(1), and NUnit runs SetUp, the test body, and TearDown on the same thread, so the capture lines up with the thread executing the test method. Background merge threads never run SetUp, so they correctly see a null test thread and are excluded.