[syahra712]

Pull Request Checklist

• 🧪 Added tests for changed code.
• 🛠️ All tests pass when run locally (run tox or make test to find out!).
• 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• 📚 Updated documentation for changed code. (n/a, bug fix)
• ⏩ Code is up-to-date with the master branch.

Description of Changes

With a single granularity="month" or "quarter", humanize divided the elapsed seconds by a fixed 30.5-day month (91.5-day quarter). Whole calendar months were then under-counted:

>>> a = arrow.Arrow(2023, 1, 1)
>>> a.shift(months=2).humanize(a, granularity="month")
'in a month'        # 59 days / 30.5
>>> a.shift(months=6).humanize(a, granularity="month")
'in 5 months'
>>> a.shift(months=3).humanize(a, granularity="quarter")
'in 0 quarters'

The "auto" granularity already counts calendar months with relativedelta. This change does the same for the single month and quarter granularities. The partial month is added as a fraction of the next calendar month, so it stays below 1 and keeps the "ago"/"in" direction when the count is 0 (e.g. Jan 1 → Jan 31 23:59 is still "0 months ago").

Multi-granularity lists are not changed here. #1367 handles those separately.

Tests

• New test_granularity_calendar_months checks 1/2/6 months and 3/6/18-month quarters from Jan 31 (with month-end clamping), plus the "0 months" case for a span longer than 30.5 days. It fails without the fix.
• One existing assertion changes: later506 is 2013-01-01 → 2014-08-02 16:53, which is 19 calendar months, not 18.
• Full suite passes: 1903 tests, coverage 99.93%. pre-commit (black, flake8, isort, mypy) is clean on the changed files.

AI-assisted (Claude): I used it to help read the code and draft the test. I reviewed and ran everything myself.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (2224255) to head (4cd57c1).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1391   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2315      2321    +6     
  Branches       358       358           
=========================================
+ Hits          2315      2321    +6     

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