Refactor tests/groupby/**

[ttnghia]

No change in code/implementation by this PR. It only renames the test files in the folder tests/groupby. In particular:

• It removes the prefixes group_ and groupby_ from all the file names in that folder.
• The file suffix _test.cpp is changed to _tests.cpp to enforce consistency with other test files.

The reasons for doing this PR are:

• Files in this folder have inconsistent prefixes (group_ and groupby_).
• Adding folder name (groupby_ or group_) as prefixes to the test files is not necessary. Those tests are already in the folder name groupby.
• We should enforce consistency following the cudf dev guide: https://github.com/rapidsai/cudf/blob/branch-0.19/cpp/docs/TESTING.md#directory-and-file-naming.

[codecov]

Codecov Report

Merging #7604 (8e3a999) into branch-0.20 (51336df) will increase coverage by 0.02%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           branch-0.20    #7604      +/-   ##
===============================================
+ Coverage        82.88%   82.91%   +0.02%     
===============================================
  Files              103      103              
  Lines            17668    17863     +195     
===============================================
+ Hits             14645    14811     +166     
- Misses            3023     3052      +29     

Impacted Files	Coverage Δ
python/cudf/cudf/core/abc.py	91.66% <ø> (+0.17%)	⬆️
python/cudf/cudf/core/algorithms.py	82.35% <ø> (ø)
python/cudf/cudf/core/column/__init__.py	100.00% <ø> (ø)
python/cudf/cudf/core/column/categorical.py	92.37% <ø> (+0.13%)	⬆️
python/cudf/cudf/core/column/column.py	88.20% <ø> (-0.44%)	⬇️
python/cudf/cudf/core/column/datetime.py	88.03% <ø> (-1.88%)	⬇️
python/cudf/cudf/core/column/decimal.py	90.29% <ø> (-2.64%)	⬇️
python/cudf/cudf/core/column/interval.py	91.66% <ø> (+0.55%)	⬆️
python/cudf/cudf/core/tools/datetimes.py	80.42% <0.00%> (-4.11%)	⬇️
... and 27 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7623f39...8e3a999. Read the comment docs.

[ttnghia]

Rerun tests.

[devavret]

• Their names (group_ and groupby_) already show such inconsistency.

This is intentional. group_ prefix is for the aggregation. group_max_test is a test that checks our ability to get each "group's max". groupby_ prefix is only meant for keys. It is a test of our ability to "group by different key types". The only inconsistency is in groupby_groups_test which was added later.

[ttnghia]

• Their names (group_ and groupby_) already show such inconsistency.

This is intentional. group_ prefix is for the aggregation. group_max_test is a test that checks our ability to get each "group's max". groupby_ prefix is only meant for keys. It is a test of our ability to "group by different key types". The only inconsistency is in groupby_groups_test which was added later.

Do you mean only groupby_groups_test needs to be renamed, the other files must remain intact?

[devavret]

the other files must remain intact?

I was just explaining the rationale behind the original names. If they still make sense with a smaller name then we should have a smaller name.

[mythrocks]

I think I should push this ASAP so other people can sync ASAP.

Curious: Why is this urgent?

[ttnghia]

Not "urgent", just in case somebody is adding new test files to this folder then they can avoid adding those prefixes, so I can avoid refactoring again their files in the future when I merge my PR.

[ttnghia]

the other files must remain intact?

I was just explaining the rationale behind the original names. If they still make sense with a smaller name then we should have a smaller name.

Thanks for your comment. Then we need to change the file names, since those files are already in the groupby folder, which means they belong to groupby.

[mythrocks]

Not "urgent", just in case somebody is adding new test files...

I wonder if it might be acceptable to reserve aesthetic/compliance changes for branch-0.20, given how close we are to branch-0.19 burn-down.
This sort of thing will cause last minute churn for those making material changes to group-by tests.

[ttnghia]

I don't think it will affect anything, as it only renames files instead of changing any implementation.

[ttnghia]

Moved this PR to v0.20 release to avoid extra work for the team as v0.19 is near its burn-down stage.

[karthikeyann]

After #7387, this PR require more tests files renamed.

[harrism]

@gpucibot merge