TST: Add tests for observance rules in holiday.py

[leonarduschen]

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• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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None of the observance rules (e.g. next_workday, before_nearest_workday) are tested

[ivanovmg]

take

[ivanovmg]

I guess that there are tests for those in pandas/tests/tseries/holiday/test_observance.py.
I added several cases for next_workday and before_nearest_workday (I guess all possible cases) in the PR #38215, but there are other observance rules, which can be covered with more cases as well.

[mroeschke]

Looks like pandas/tests/tseries/holiday/test_observance.py has been pretty fleshed out in the meantime to meet the spirit of the original issue so closing. Can open a new issue with specific items if there are followups