[jira] [Commented] (ARROW-13013) [C++][Compute][Python] Move (majority of) kernel unit tests to python

["Eduardo Ponce (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-13013?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17359492#comment-17359492 ] 

Eduardo Ponce commented on ARROW-13013:
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What implications would this have on C++-only builds?

> [C++][Compute][Python] Move (majority of) kernel unit tests to python
> ---------------------------------------------------------------------
>
>                 Key: ARROW-13013
>                 URL: https://issues.apache.org/jira/browse/ARROW-13013
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++, Python
>            Reporter: Ben Kietzman
>            Priority: Major
>
> mailing list discussion: https://lists.apache.org/thread.html/r09e0e0fbb8b655bbec8cf5662d224f3dfc4fba894a312900f73ae3bf%40%3Cdev.arrow.apache.org%3E
> Writing unit tests for compute functions in c++ is laborious, entails a lot of boilerplate, and slows iteration since it requires recompilation when adding new tests. The majority of these test cases need not be written in C++ at all and could instead be made part of the pyarrow test suite.
> In order to make the kernels' C++ implementations easily debuggable from unit tests, we'll have to expose a c++ function named {{AssertCallFunction}} or so. {{AssertCallFunction}} will invoke the named compute::Function and compare actual results to expected without crossing the C++/python boundary, allowing a developer to step through all relevant code with a single breakpoint  in GDB. Construction of scalars/arrays/function options and any other inputs to the function is amply supported by {{pyarrow}}, and will happen outside the scope of {{AssertCallFunction}}.
> {{AssertCallFunction}} should not try to derive additional assertions from its arguments - for example {{CheckScalar("add", {left, right}, expected)}} will first assert that {{left + right == expected}} then {{left.slice(1) + right.slice(1) == expected.slice(1)}} to ensure that offsets are handled correctly. This has value but can be easily expressed in Python and configuration of such behavior would overcomplicate the interface of {{AssertCallFunction}}.
> NB: Some unit tests will probably still reside in C++ since we'll need to test things we don't wish to expose in a user facing API, such as "whether a boolean kernel avoids clobbering bits when outputting into a slice". These should be far more manageable since they won't need to assert correct logic across all possible input types



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