expand non_fitted_error_checks for methods get_feature_names_out and inverse transform

[solegalli]

Methods transform, inverse_transform, get_feature_names_out and other specific methods (see DropMissingData) should run only after the transformer was fit.

At the moment, we test that this is the case only for the transform method. We should expand this to test all methods.

[solegalli]

Checks for get_feature_names_out were taken care of in #519

[Morgan-Sell]

@solegalli,

Is this as simple as adding check_is_fitted(self) to the abovementioned methods?

[solegalli]

Nothing is as simple as it looks @Morgan-Sell lol

We basically need to ensure that we have what you say in all methods across all transformers, and then make a test, and ensure we test all transformers.

I am thinking about refactoring the way we test. It seems to be readable only to me, lol. I tried to copy what sklearn is doing, but I am not pleased with the outcome. So, this is not a simple one unfort.

[Morgan-Sell]

@solegalli, you had me at "refactoring the way we test." Although, I don't know what's wrong with our current approach. How are you thinking we design our tests?

[solegalli]

I am entertaining the idea of having individual tests in check_estimators, but instead of then summoning all tests within a master test, which we then summon from the test_estimators.py for all transformers, we should just run them from each transformer test script individually.

Hard to explain without going over the scripts. But I'd like it to be clear for each user which tests are being run for each transformer, and I would like to avoid adding tags as we do now, as much as possible

[TemidayoA]

Opened #953 covering the inverse_transform half of this — the shared check now calls inverse_transform on an unfitted clone (accepting NotImplementedError for the transformers that deliberately don't support inversion). All transformers get covered automatically through check_feature_engine_estimator. Happy to adjust if you'd prefer this shaped differently given the test-refactor plans discussed above.