TST: Fix a doctest in style_render.py

[aneesh98]

Fix the following doctest in style_render.py file:

pandas/io/formats/style_render.py F

=================================== FAILURES ===================================
________ [doctest] pandas.io.formats.style_render.StylerRenderer.format ________
647 
648         >>> df = pd.DataFrame([[np.nan, 1.0, 'A'], [2.0, np.nan, 3.0]])
649         >>> df.style.format(na_rep='MISS', precision=3) # doctest: +SKIP
650                 0       1       2
651         0    MISS   1.000       A
652         1   2.000    MISS   3.000
653 
654         Using a ``formatter`` specification on consistent column dtypes
655 
656         >>> df.style.format('{:.2f}', na_rep='MISS', subset=[0,1])
Expected:
            0      1          2
    0    MISS   1.00          A
    1    2.00   MISS   3.000000
Got:
    <pandas.io.formats.style.Styler object at 0x7f77b214ea30>

/home/aneesh/Desktop/Side Projects/ops/pandas/pandas/io/formats/style_render.py:656: DocTestFailure
- generated xml file: /home/aneesh/Desktop/Side Projects/ops/pandas/test-data.xml -
============================= slowest 30 durations =============================
1.14s call     pandas/io/formats/style_render.py::pandas.io.formats.style_render.StylerRenderer.format

(2 durations < 0.005s hidden.  Use -vv to show these durations.)
=========================== short test summary info ============================
FAILED pandas/io/formats/style_render.py::pandas.io.formats.style_render.StylerRenderer.format
============================== 1 failed in 1.70s ===============================

---

OBSERVATION

The mentioned test returns a Styler object which will render properly in (for instance, a notebook), but will fail the doctest as it will simply return the object.

SOLUTION

Add images of output rendered, in the doctest wherever required. (The approach is mentioned #42674 (comment), for the documentation of background_gradient()) or add a # doctest: +SKIP if necessary.

[aneesh98]

take

[attack68]

Styler is a different object to the rest of pandas, its methods affect the visual output of browsers and other renderers.

These docstrings were created as a balance between helping the user and being able to read the code as a developer.

Adding images has the disadvantage of being more difficult for developers to edit, but being visually accurate.
The doc test as is has the advantages of being editable by devs and visible to users, but the disadvantage of failing a doc test.

The soultion here, as is with many styler doc tests is to skip it.

[aneesh98]

Thank you so much for the feedback @attack68