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From Michael McCandless <>
Subject Re: failure in TestTrieRangeQuery
Date Wed, 04 Feb 2009 11:01:54 GMT


I was wondering (but didn't dig) whether we could extend  
LuceneTestCase to expose a getRandom() method (which'd record the  
seed), and then override invocation of a test (which I'm not sure  
JUnit allows you to do) to add a try/finally that prints out the seeds.

Though: I thought JUnit invokes tests in the sequential order as they  
are defined in your class?  (I'm not sure about this... it's just what  
seems to be the case).  And even if it is the case, it's not clear  
that's guaranteed as part of JUnit's "contract".  If it isn't, we  
could have getRandom take a String name and then on exception we print  
out the full name -> seed for all getRandom calls for that test?

I'd like to to find a simple common API, if we can, so that we can fix  
all tests that use Random to use it... though really the mods you had  
to make are fairly minimal, so we could simply adopt that per test too.


Uwe Schindler wrote:

> Hi,
>>> : 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.
>> I agree, it's frustrating.  But I'd prefer to know the bug is there
>> and then
>> writhe in frustration at not being able to reproduce it very easily,
>> then let
>> the bug go undetected.  I guess ignorance is not bliss, for me ;)
>>> 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
>> +1!  I like this approach.  We could record the seed up front, and
>> then in
>>  a try/finally if the test failed, print the seed.
> I implemented this for TestTrieRangeQuery (see patch). I catch
> java.lang.Error and print the random seed recorded before (The seed is
> generated by a static Random instance for each test method in  
> separate:
> Because you cannot predict the order of tests, each test method  
> should have
> its own Random instance). As both the Java 1.4 AssertionError and  
> the jUnit
> AssertionFailedError are subclasses of Error, they can be catched and
> rethrown easily.
> Uwe
> <random-trie- 
> test 
> .patch 
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