[CI] test_kernel_density fails with NotImplementedError validation issues

[csadorf]

Summary

The test_kernel_density property-based test is failing due to two issues: the error message for an expected NotImplementedError does not match the expected string, and in some cases, a NotImplementedError is not raised when it should be.

Failing test/component: test_kernel_density.py::test_kernel_density

Failure observed in:

• https://github.com/rapidsai/cuml/actions/runs/18904547567/job/53979841580 (ubuntu22.04, Python 3.11, latest-deps)
• https://github.com/rapidsai/cuml/actions/runs/18904547567/job/53979841602 (rockylinux8, Python 3.10, oldest-deps)
• and others

Environment

This failure is environment-independent and occurs regardless of OS, Python version, CUDA version, GPU, or dependency set.

Test Details

• Test file: python/cuml/tests/test_kernel_density.py
• Test name: test_kernel_density (line 96)
• Error message:

  BaseExceptionGroup: Hypothesis found 2 distinct failures. (2 sub-exceptions)
  
  Failure 1 - Regex pattern mismatch:
    Expected: "Only \['gaussian', 'tophat'\] kernels, and the euclidean metric are supported."
    Actual: "Only ['gaussian', 'tophat'] kernels are supported."
    Example: kernel='epanechnikov', metric='euclidean'
  
  Failure 2 - Missing validation:
    Expected: NotImplementedError to be raised
    Actual: No error raised
    Example: kernel='gaussian', metric='manhattan'
  

Root Cause Analysis