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https://issues.apache.org/jira/browse/LUCENE-1535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12670444#action_12670444
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Michael McCandless commented on LUCENE-1535:
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bq. The @link reference in the javadocs to LuceneTestCase reference
#getRandom(long) not #newRandom(long)
No problem, I'll fix. Thanks!
bq. if in future jUnit changes not to create new instances for each test
Heh -- I had assumed it did NOT create a new instance for each test, but in
fact you're right: it does.
> Make tests using java.util.Random reproducible on failure
> ---------------------------------------------------------
>
> Key: LUCENE-1535
> URL: https://issues.apache.org/jira/browse/LUCENE-1535
> Project: Lucene - Java
> Issue Type: Test
> Affects Versions: 2.9
> Reporter: Uwe Schindler
> Assignee: Michael McCandless
> Fix For: 2.9
>
> Attachments: LUCENE-1535.patch, LUCENE-1535.patch
>
>
> This is a patch for LuceneTestCase to support logging of the Random seed used
> in randomized tests. The patch also includes an example implementation in
> TestTrieRangeQuery.
> It overrides the protected method runTest() and inserts a try-catch around
> the super.runTest() call. Two new methods newRandom() and newRandom(long) are
> available for the test case. As each test case is run in an own TestCase
> object instance (so 5 test methods in a class instantiate 5 instances each
> method working in separate), the random seed is saved on newRandom() and when
> the test fails with any Throwable, a message with the seed (if not null) is
> printed out. If newRandom was never called no message will be printed.
> This patch has only one problem: If a single test method calls newRandom()
> more than once, only the last seed is saved and printed out. But each test
> method in a Testcase should call newRandom() exactly once for usage during
> the execution of this test method. And it is not thread save (no sync, no
> volatile), but for tests it's unimportant.
> I forgot to mention: If a test fails, the message using the seed is printed
> to stdout. The developer can then change the test temporarily:
> {code}LuceneTestCase.newRandom() -> LuceneTestCase.newRandom(long){code}
> using the seed from the failed test printout.
> *Reference:*
> {quote}
> : By allowing Random to randomly seed itself, we effectively test a much
> : much larger space, ie every time we all run the test, it's different. We
> can
> : potentially cast a much larger net than a fixed seed.
> i guess i'm just in favor of less randomness and more iterations.
> : Fixing the bug is the "easy" part; discovering a bug is present is where
> : we need all the help we can get ;)
> yes, but knowing a bug is there w/o having any idea what it is or how to
> trigger it can be very frustrating.
> it would be enough for tests to pick a random number, log it, and then use
> it as the seed ... that way if you get a failure you at least know what
> seed was used and you can then hardcode it temporarily to reproduce/debug
> -Hoss
> {quote}
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