Re: [DISCUSS] HADOOP-9122 Add power mock library for writing better unit tests

[Chris Douglas <cd...@apache.org>]

Eric-

It might be easier to grok the benefits of Powermock if you wrote an
example test. As you say, starting a mini*cluster to test input
validation is wasteful, but it's not clear why that would be required
if Powermock were unavailable.

It's not a huge deal to add a dependency, particularly if it improves
our tests. However, "constructor suppression, inner class replacement
and private method override" are aggressive workarounds. These might
be justifiable for testing with a third-party library, but in our
setting it's more likely a sign of a suboptimal design. Some of these,
particularly "private method override" sound like they'll create more
brittle tests, rather than more testable code.

However, if there are some cases where Hadoop is forcing bad design
because of some existing, pervasive code, then maybe judicious use of
Powermock could help. -C


On Fri, Sep 29, 2017 at 2:46 PM, Eric Yang <ey...@hortonworks.com> wrote:
> Hi Chris and Andrew,
>
>
>
> The intend is for new code to have better unit test cases without resort to
> invocation of miniHDFSCluster or miniYarnCluster.  Existing code don’t
> require refactoring, if the test cases already have good coverages.  I am
> currently working on part of YARN to improve YARN and Docker integration.
> There are a lot of code getting triggered for UGI, FileSystem object to Yarn
> job submission.  My code is only responsible to check the logic of the user
> input, and expected output prior to YarnClient job submission.  Starting a
> miniCluster for this test case is excessive for the small piece of code for
> validation.  The submission code was imported from Slider for YARN native
> services, a single class imports various Hadoop services.  In several
> failure cases, it is difficult to simulate exact error conditions because
> the API is several layers deep.  Powermock provides easy way to replace and
> stubbing return object or throw proper exception to simulate the failure
> conditions.  One can argue that the code should have been written easier for
> unit tests, but Hadoop code density is beyond trivial to get simple
> initialization done.  Constructor suppression, inner class replacement and
> private method override are good tools from Powermock that can provide more
> accurate testing without losing sights of multiple stage API calling tests
> while keeping the test case localized to a small piece of the greater
> puzzle.  Hence, I like to request the community to rethink the improvement
> that Powermock can bring to the table.  Thank you for your considation.
>
>
>
> Regards,
>
> Eric
>
>
>
> From: Andrew Wang <an...@cloudera.com>
> Date: Friday, September 29, 2017 at 1:55 PM
> To: Chris Douglas <cd...@apache.org>
> Cc: Eric Yang <ey...@hortonworks.com>, "common-dev@hadoop.apache.org"
> <co...@hadoop.apache.org>
> Subject: Re: [DISCUSS] HADOOP-9122 Add power mock library for writing better
> unit tests
>
>
>
> Making code testable is about a lot more than your mocking library. In HDFS,
> the NameNode is very monolithic, so it's hard to instantiate little pieces
> of functionality in isolation and mock things out. I have my doubts that
> Powermock will help with this unless someone's willing to invest in
> significant refactoring effort of our existing code and unit test suites.
>
>
>
> I could see an argument of this being useful for new code being developed,
> but like Chris, I'd like to see an example of where Mockito falls short, and
> what additional capabilities Powermock brings to the table.
>
>
>
> Best,
>
> Andrew
>
>
>
> On Fri, Sep 29, 2017 at 10:38 AM, Chris Douglas <cd...@apache.org> wrote:
>
> Eric-
>
> Can you explain how Powermock differs from/augments Mockito, why we
> should adopt it, and maybe an example of an existing test that could
> be improved using this library? -C
>
>
> On Fri, Sep 29, 2017 at 10:12 AM, Eric Yang <ey...@hortonworks.com> wrote:
>> Hi Hadoop-dev,
>>
>> Long time ago, Hadoop community decided to put Powermock on hold for unit
>> tests.  Both mockito and powermock has evolved a lot in the past 5 years.
>> There are mature versions of both software, and there are compatibility
>> charts to indicate which versions can work together.  Hadoop has grown a lot
>> in the last 5 years.  It becomes apparent that without ability to instrument
>> lower level classes to contain unit test scope.  Many tests are written to
>> simulate integration test in order to perform unit tests.  The result is
>> slow performance on unit tests, and some parts are not testable strictly in
>> unit test case.  This discussion is to revisit the decision, and see if we
>> would embrace Powermock and allow HADOOP-9122 to be implemented.  Feel free
>> to comment on HADOOP-9122 and this thread to revisit this issue.
>>
>> Thank you for your time.
>>
>> Regards,
>> Eric
>
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