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From David Hall <d...@cs.stanford.edu>
Subject Re: Testing Mappers in Hadoop 0.20.0
Date Thu, 23 Jul 2009 00:29:12 GMT
This is nice, but doesn't it suffer from the same problem? MRUnit uses
the mapred API, which is deprecated, and the new API doesn't use
OutputCollector, but a non-static inner class.

-- David

On Wed, Jul 22, 2009 at 4:52 PM, Aaron Kimball<aaron@cloudera.com> wrote:
> Hi David,
> I wrote a contrib module called MRUnit
> (http://issues.apache.org/jira/browse/hadoop-5518) designed to allow
> unit tests for mappers/reducers more easily. It's slated for inclusion
> in 0.21, not 0.20 unfortunately, but you can download the patch above
> as well as MAPREDUCE-680 and build it against any earlier version of
> Hadoop. Unfortunately, it doesn't currently support the new APIs
> (e.g., with Context objects), but I imagine this could be added with
> little difficulty. I just haven't had time to do it myself ;) If you'd
> like to take a stab at it, I'd love some help!
> More info is at www.cloudera.com/hadoop-mrunit
> Cheers,
> - Aaron
> On Wed, Jul 22, 2009 at 2:49 PM, David Hall<dlwh@cs.stanford.edu> wrote:
>> Hi,
>> I'm a student working with Apache Mahout for the Google Summer of
>> Code. We recently moved to 0.20.0, and I was porting my code to the
>> new API. Unfortunately, I (and the whole project team) seem to have
>> run into a problem when it comes to testing them.
>> Historically, we would create a Mapper in a unit test, and a special
>> "DummyOutputCollector", which was essentially a multimap dressed up to
>> conform to OutputCollector. In Hadoop 0.20.0, this isn't possible
>> anymore, because Mappers take an instance of an inner class.
>> It's of course possible to dress up the Context in something else
>> (say, something just like an OutputCollector), and to specify that
>> Mahout Mappers should just delegate to a method that takes an
>> OutputCollector. But, this seems to not be very idiomatic.
>> All this goes to say, what would be a "best practice" for testing
>> Mappers and Reducers in 0.20.0?
>> Thanks,
>> David Hall

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