test(development): assert exclusions-ignored UserWarning in drop tests (#765)

[SaguaroDev]

Closes #765.

Per @kennethshsu's call on the issue thread to use pytest.warns uniformly and not blanket-silence with @pytest.mark.filterwarnings, this wraps each .fit() / ._set_weight_func() call that emits UserWarning: "Some exclusions have been ignored..." in pytest.warns(UserWarning, match="exclusions have been ignored").

This makes the contract explicit at each call site: the test fails if the warning stops firing OR if its message changes. The two calls in test_drophighlow that don't warn (drop_high=0 and drop_high=[T,F,T,F]) were left untouched, since wrapping them would assert a warning that doesn't fire.

Affected tests

chainladder/development/tests/test_development.py:

• test_drophighlow — wrapped 5 of 7 .fit() calls (the two that don't warn left as-is)
• test_new_drop_5 — wrapped the single .fit()
• test_new_drop_5a — wrapped both _set_weight_func calls (factored out lhs/rhs locals for the pytest.warns blocks)
• test_new_drop_7 — wrapped the single .fit()
• test_pipeline — wrapped both dev1 and pipeline .fit()

chainladder/development/tests/test_incremental.py:

• test_pipeline — wrapped both dev1 and pipeline .fit(); added import pytest

Verification

Local run on the branch:

671 passed, 12 xfailed (pre-existing)

Targeted pytest chainladder/development/tests/ warning-summary count for "exclusions have been ignored" drops from 10 to 4. The remaining 4 are pytest's source-line accounting from inside the pytest.warns blocks (deduplicated by warning location), not leaked warnings — running pytest -W "error::UserWarning" on the targeted set still passes, confirming no warnings escape the context managers.

Out of scope

Other warning families flagged in #765 (e.g. X and sample_weight not aligned, accumulate-overflow RuntimeWarnings, infer-format) are deliberately not touched here. Happy to file follow-up issues if the maintainers want them addressed individually.

---

Note

Low Risk
Low risk: changes are limited to tests and clarifying comments around an existing UserWarning message, with no changes to development calculation logic.

Overview
Tests now explicitly assert the existing UserWarning emitted when preserve forces exclusions to be ignored by wrapping affected .fit() / ._set_weight_func() calls in pytest.warns(..., match="exclusions have been ignored") (including pipeline tests for both Development and IncrementalAdditive).

DevelopmentBase adds inline notes next to each warning site to prevent accidental edits to the warning text or removal of warnings.warn(...) without updating the test matchers.

^{Reviewed by Cursor Bugbot for commit 44decd5. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.08%. Comparing base (f8dd20b) to head (44decd5).
⚠️ Report is 16 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #777   +/-   ##
=======================================
  Coverage   86.08%   86.08%           
=======================================
  Files          86       86           
  Lines        4923     4924    +1     
  Branches      638      638           
=======================================
+ Hits         4238     4239    +1     
  Misses        486      486           
  Partials      199      199           

Flag	Coverage Δ
unittests	86.08% <100.00%> (+<0.01%)	⬆️

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[henrydingliu]

can we add a comment to the source code that the warning is tied to unit test and should not be modified without due consideration?

[SaguaroDev]

Done in 44decd5. Added a NOTE comment above each of the four if warning_flag: blocks in chainladder/development/base.py (sites in _drop_n, _drop_x, _drop_valuation_x, and _drop_n_func), explaining that the "Some exclusions have been ignored..." message is matched by pytest.warns(..., match="exclusions have been ignored") in test_development.py / test_incremental.py, and that changes to the wording or removal of the warnings.warn(...) call require updating the test matchers. Comment-only, no behavior change.