feat: raise ValueError when variables and missing_only=True are used together in AddMissingIndicator and DropMissingData

[direkkakkar319-ops]

Description

Fixes #905

Makes variables and missing_only=True mutually exclusive in both AddMissingIndicator and DropMissingData. Previously, passing both silently produced confusing behaviour — variables with no missing data would be quietly dropped from the output with no indication to the user.

Changes

feature_engine/imputation/missing_indicator.py

• Added ValueError in __init__() when variables is not None and missing_only=True
• Updated docstrings for variables and missing_only to document mutual exclusivity

feature_engine/imputation/drop_missing_data.py

• Same validation and docstring updates

tests/test_imputation/test_missing_indicator.py

• 3 new tests: raises on invalid combo, valid with missing_only=False, valid with variables=None
• Updated existing tests that implicitly relied on default missing_only=True alongside variables

tests/test_imputation/test_drop_missing_data.py

• Same 3 new tests
• Same existing test updates

docs/whats_new/v_190.rst

• Changelog entry added

Type of Change

• Bug fix
• New feature (non-breaking)
• Breaking change
• Documentation update

Tests

pytest tests/test_imputation/test_missing_indicator.py tests/test_imputation/test_drop_missing_data.py
23 passed

Notes

• Default behaviour (variables=None, missing_only=True) is completely unchanged
• Users passing both variables and missing_only=True now get a clear ValueError instead of silent unexpected output

[direkkakkar319-ops]

Hi @solegalli
All 13 CI checks are green, including test_style, test_type, and all Python/sklearn matrix builds.
This PR is ready for your review. Happy to make any changes based on your feedback!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.27%. Comparing base (f72a2b7) to head (dc34edf).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #912   +/-   ##
=======================================
  Coverage   98.27%   98.27%           
=======================================
  Files         116      116           
  Lines        4978     4996   +18     
  Branches      795      804    +9     
=======================================
+ Hits         4892     4910   +18     
  Misses         55       55           
  Partials       31       31           

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[direkkakkar319-ops]

@solegalli, @ankitlade12 Hi! I'm facing issues with the two failing codecov checks on this PR:

• codecov/patch: Currently at 93.33% but the target is 98.27%
• codecov/project: Dropped by 0.04% compared to f72a2b7

Could you help me understand:

1. Which specific lines/files are not covered by tests?
2. Are there any existing tests I can extend, or should I add new test cases?

I want to bring the patch coverage up to meet the target. Any guidance would be appreciated.

[solegalli]

Hey @direkkakkar319 Thank you so much for all PRs and issues on feature-engine. I really appreciate your contributions and motivation! I am currently on the last weeks of travel, so had very little time and internet connection to look at them in detail. I will come back to you with some comments from 21st march. Sorry for the delay and thanks for the patience! Sent from [Proton Mail](https://proton.me/mail/home) for iOS.

…

Message ID: ***@***.***>

[direkkakkar319-ops]

Hey @solegalli,no worries at all ,take your time! I hope you're enjoying your travels.
I'll also take the opportunity to look into the 2 failing checks before you're back, and will try to get those resolved.Looking forward to your feedback on the 21st. Thanks again

[direkkakkar319-ops]

there were few local file that were push to this branch , I removed them

[direkkakkar319-ops]

Fixed the Codecov patch coverage failure by adding a missing test for the errors='warn' branch in the single variable path of CategoricalImputer. This branch was previously not being hit by any test

all the test cases have also passed

the 15CI checks including the 2 codecov checks have also passes

changes file :-
tests/test_imputation/test_categorical_imputer.py