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https://issues.apache.org/jira/browse/MRUNIT-158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13497849#comment-13497849
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Bertrand Dechoux commented on MRUNIT-158:
-----------------------------------------
Like I said, for MapWritable the toString()/equals()/hashcode() methods were
not overrided in the implementation.
This implies that
1) if the toString() outputs are different, then java will consider the
MapWritable instances as different. Only by reading the output of your test,
you indeed know why it is failing. (e1 =! 2059)
2) even if two MapWritable instances have exactly the same content (which
implies that they should be equals according the java Map contract), they won't
in practice actually be equal
A solution for MRunit could be to provide our own equal implementation that
should be used only when the class of the key/value is an instance of
MapWritable but that would means MRUnit behaviour will differ from the standard
Hadoop behaviour. Introducing such potential bugs in a testing library is dodgy.
MRunit could also provide a custom toString() method using the same mechanism
but that would render the test less explicit when comparing two MapWritable
instances with the same content. The toString() output will be the same but
that instances won't be equals. That would also be quite confusing.
Of course, MRunit is an apache project, you are welcome to correct me. And if
you have a solution, you are also welcome to provide it or at least outline it.
For me, from the user point of view, the solution is to not use MapWritable.
Sure, they are handy and that would be great if they were actually respecting
the java Map contract but that's not the case as of now. And from a performance
point of view, maps are not ideally because you are transporting a (untyped)
schema for each instance.
> withOutput doesn't generate useful information with MapWritable on error
> ------------------------------------------------------------------------
>
> Key: MRUNIT-158
> URL: https://issues.apache.org/jira/browse/MRUNIT-158
> Project: MRUnit
> Issue Type: Improvement
> Affects Versions: 0.9.0
> Reporter: Patrick Hunt
> Priority: Minor
>
> Using withOutput generates the following, notice that the hashcode is printed
> rather than some useful detail as to the content of the maps:
> Nov 9, 2012 2:40:01 PM org.apache.hadoop.mrunit.TestDriver logError
> SEVERE: Missing expected output (null-0, org.apache.hadoop.io.MapWritable@e1)
> at position 0.
> Nov 9, 2012 2:40:01 PM org.apache.hadoop.mrunit.TestDriver logError
> SEVERE: Received unexpected output (null-0,
> org.apache.hadoop.io.MapWritable@2059) at position 0.
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