DOC: Test doctests in pandas/core/groupby/groupby.py

[HyukjinKwon]

• closes GroupBy.mean() doctests failed due to comparison to nothing #26254
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #26255 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26255      +/-   ##
==========================================
- Coverage   91.98%   91.97%   -0.01%     
==========================================
  Files         175      175              
  Lines       52384    52384              
==========================================
- Hits        48184    48179       -5     
- Misses       4200     4205       +5

Flag	Coverage Δ
#multiple	90.52% <ø> (ø)	⬆️
#single	40.72% <ø> (-0.14%)	⬇️

Impacted Files	Coverage Δ
pandas/core/groupby/groupby.py	97.23% <ø> (ø)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	96.9% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.61% <0%> (-0.11%)	⬇️

---

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[codecov]

Codecov Report

Merging #26255 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26255      +/-   ##
==========================================
- Coverage   91.98%   91.97%   -0.02%     
==========================================
  Files         175      175              
  Lines       52384    52386       +2     
==========================================
- Hits        48184    48180       -4     
- Misses       4200     4206       +6

Flag	Coverage Δ
#multiple	90.52% <ø> (-0.01%)	⬇️
#single	40.72% <ø> (-0.14%)	⬇️

Impacted Files	Coverage Δ
pandas/core/groupby/groupby.py	97.23% <ø> (ø)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/base.py	97.98% <0%> (-0.22%)	⬇️
pandas/core/frame.py	96.9% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.61% <0%> (-0.11%)	⬇️

---

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[jreback]

this is probably a good fix, but we are not testing this currently, you need update in ci/code_checks (and see if this passes)

    MSG='Doctests generic.py' ; echo $MSG
    pytest -q --doctest-modules pandas/core/generic.py \
        -k"-_set_axis_name -_xs -describe -droplevel -groupby -interpolate -pct_change -pipe -reindex -reindex_axis -to_json -transpose -values -xs -to_clipboard"
    RET=$(($RET + $?)) ; echo $MSG "DONE"

[HyukjinKwon]

Thanks for your guidance.

[datapythonista]

lgtm

Feel free to fix the doctests in cumcount, describe, pipe in this PR if you want. But happy to merge this and take care of them later.

[jreback]

thanks for the patch @HyukjinKwon keep em coming!