[ENH] Extend Extension class test suite

[satvshr]

Metadata

• Reference Issue: fixes [ENH] Extension Module Tests (or Examples?) #1545
• New Tests Added: Yes
• Documentation Updated: No
• Change Log Entry: Add tests for extension interface contract and extension registry edge cases

Details

• What does this PR implement/fix? Explain your changes.
  This PR adds unit tests for the OpenML Extension interface and for extension registry behavior. The tests added are the 7 tests mentioned in [ENH] Extension Module Tests (or Examples?) #1545
• Why is this change necessary? What is the problem it solves?
  Previously, only the non-abstract registry helpers (get_extension_by_model, get_extension_by_flow) were covered. The abstract Extension interface itself was not tested.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.72%. Comparing base (c5f68bf) to head (e8c64f2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1560      +/-   ##
==========================================
- Coverage   53.02%   52.72%   -0.31%     
==========================================
  Files          36       36              
  Lines        4326     4326              
==========================================
- Hits         2294     2281      -13     
- Misses       2032     2045      +13     

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[satvshr]

Error seems unrelated to the PR given all this PR does is extend the Extension class. The failing test:

    @pytest.mark.sklearn()
    @unittest.skipIf(
        Version(sklearn.__version__) == Version("0.19.1"),
        reason="Requires scikit-learn!=0.19.1, because target flow is from that version.",
    )
    @pytest.mark.production()
    def test_get_flow_with_reinstantiate_strict_with_wrong_version_raises_exception(self):
        self.use_production_server()
        flow = 8175
        expected = "Trying to deserialize a model with dependency sklearn==0.19.1 not satisfied."
        self.assertRaisesRegex(
            ValueError,
            expected,
            openml.flows.get_flow,
            flow_id=flow,
            reinstantiate=True,
            strict_version=True,
        )

Edit: The tests pass locally.

[jgyasu]

Looks good to me. I think we can merge this even if the the Extension is planned to be refactored.