[BUG] ensure BaseMetaObject resets at set_params; add 'test_set_params_resets_fitted_state' test to trigger error

[SimonBlanke]

Reference Issues/PRs

fixes #412

What does this implement/fix? Explain your changes.

This PR adds a test to trigger the bug described in #412. If desired this PR will also add a fix to the bug.

Does your contribution introduce a new dependency? If yes, which one?

What should a reviewer concentrate their feedback on?

Any other comments?

PR checklist

For all contributions

• I've reviewed the project documentation on contributing
• I've added myself to the list of contributors.
• The PR title starts with either [ENH], [CI/CD], [MNT], [DOC], or [BUG] indicating whether
  the PR topic is related to enhancement, CI/CD, maintenance, documentation, or a bug.

For code contributions

• Unit tests have been added covering code functionality
• Appropriate docstrings have been added (see documentation standards)
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[SimonBlanke]

One problem in #413 is, that reset is called multiple times in some instances. It would be better to always have one reset. I attempt to fix this problem and the original issue in this commit 07044cb

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 86.28%. Comparing base (306958d) to head (67d6ad4).
⚠️ Report is 161 commits behind head on main.

Files with missing lines	Patch %	Lines
skbase/base/_meta.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #467      +/-   ##
==========================================
+ Coverage   85.07%   86.28%   +1.21%     
==========================================
  Files          45       50       +5     
  Lines        3015     3602     +587     
==========================================
+ Hits         2565     3108     +543     
- Misses        450      494      +44     

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[SimonBlanke]

The tests I added to trigger the bug described in the issue now pass after implementing my fix.

[fkiraly]

Brilliant!

I now understand that the return self call is the culprit.

This is unfortunate, I did spot it as an inconsistency and indeed it actually turned out (by your diagnosis) that it is the problem here.

If the clause if params is None: return self would not happen, would the issue not have happened? That is a strong indication that this special case caused a problem.

Either way, that is out of scope for this PR, but perhaps we should open an issue on whether this needs a change?

[fkiraly]

issue opened here: #469