add test to ensure estimators raise errors when X has duplicated column names

[david-cortes]

Per comment in PR: #686 (review)

After the PR in the link above gets merged, there will be a general check for duplicated columns for which a test was added in test_dataframe_checks.py. This new error raised on duplicated column names should be tested also in the invidual transformers in estimator_checks/* after the files gets refactored.

[solegalli]

Thank you @david-cortes

[Morgan-Sell]

hi @solegalli and @david-cortes,

Slowly dipping my toes back into feature-engine.

Is the idea to create a test/check function on dataframe_checks.py and then add the check functions to the parent transformers in the fit() method?

[solegalli]

No, I think the idea was to add a generic test to estimator_checks to test all transformers to ensure that they inherit this functionality properly. I am not sure if it is an overkill or not.

[Morgan-Sell]

Ok, so as the code base stands, feature-engine transformers raise errors when there are duplicative feature names, correct? This issue is to create a test that the error is being raised when expected.

[solegalli]

Correct!