[#356] RotatableWriterTest: list the archives after the rotator stops, keep only the last listing

[vharseko]

Summary

RotatableWriterTest.testAutomaticallyEvaluatesPolicesPeriodicallyIfRotationIntervalSpecified listed the archives while the rotator kept rotating the file every second, and getAllHistoricalFiles() added each listing to the previous ones. A listing taken during a rotation holds the renamed file, its .gz archive and the previous archive, which the retention check deletes only after the rotation, so the result never shrank back to one file.

• The test closes the writer before it lists the archives: close() shuts the rotator down and waits for a running rotation and retention check, so the listing sees the state that retention left.
• getAllHistoricalFiles() keeps only the last listing instead of accumulating them; the unused existingFiles parameter is gone.

Only the test changes.

Reproduction

A temporary Thread.sleep in GzipUtil.compressRotatedFile(), before the uncompressed file is deleted, widened the rotation window, and the test ran 6 times (invocationCount = 6). Neither of these is part of the PR.

Code	Rotation window	Result
master	700 ms	6/6 pass: the listing at 3 s misses the rotations
master	1200 ms	6/6 fail with Expected size: 1 but was: 3 (the renamed file, its .gz, the previous .gz) in ~4.3 s, as on CI
helper fix only	1200 ms	6/6 pass
helper fix only	1500 ms	6/6 fail: the last listing still falls into a rotation
helper fix + close()	1500 ms	6/6 pass
helper fix + close()	3000 ms	6/6 pass

Testing

• mvn -o -pl commons/audit/core -am test: 160 tests, 0 failures.
• RotatableWriterTest again after the final comment edits: 18 tests, 0 failures.

Fixes #356

[maximthomas]

praise: The fix goes where the race is: the test now lists the archives only after the rotator has stopped.

• rotatableWriter.close() runs before assertRetainedHistoricalFiles (RotatableWriterTest.java:439-444). RotatableWriter.close() calls awaitTermination on the single scheduled task that rotates the file, compresses it (GzipUtil.compressRotatedFile) and applies retention, so the listing sees a directory nothing else is changing. I injected a 1500 ms sleep into compressRotatedFile and the test passed at this head (1/1, 4.4 s).
• The reproduction table in the description shows what each half of the change does: the helper change alone still fails at 1500 ms, and the helper change plus close() passes.