MAINT Param validation: better message when common test fails to raise (

scikit-learn#26702)

sklearn/tests/test_public_functions.py

@@ -92,9 +92,16 @@ def _check_function_param_validation(
  rf"The '{param_name}' parameter of {func_name} must be .* Got .* instead."
  )
 
+ err_msg = (
+ f"{func_name} does not raise an informative error message when the "
+ f"parameter {param_name} does not have a valid type. If any Python type "
+ "is valid, the constraint should be 'no_validation'."
+ )
+
  # First, check that the error is raised if param doesn't match any valid type.
  with pytest.raises(InvalidParameterError, match=match):
  func(**{**valid_required_params, param_name: param_with_bad_type})
+ pytest.fail(err_msg)
 
  # Then, for constraints that are more than a type constraint, check that the
  # error is raised if param does match a valid type but does not match any valid
@@ -107,8 +114,19 @@ def _check_function_param_validation(
  except NotImplementedError:
  continue
 
+ err_msg = (
+ f"{func_name} does not raise an informative error message when the "
+ f"parameter {param_name} does not have a valid value.\n"
+ "Constraints should be disjoint. For instance "
+ "[StrOptions({'a_string'}), str] is not a acceptable set of "
+ "constraint because generating an invalid string for the first "
+ "constraint will always produce a valid string for the second "
+ "constraint."
+ )
+
  with pytest.raises(InvalidParameterError, match=match):
  func(**{**valid_required_params, param_name: bad_value})
+ pytest.fail(err_msg)
 
 
 PARAM_VALIDATION_FUNCTION_LIST = [

sklearn/utils/estimator_checks.py

@@ -4287,6 +4287,12 @@ def check_param_validation(name, estimator_orig):
  # the method is not accessible with the current set of parameters
  continue
 
+ err_msg = (
+ f"{name} does not raise an informative error message when the parameter"
+ f" {param_name} does not have a valid type. If any Python type is"
+ " valid, the constraint should be 'no_validation'."
+ )
+
  with raises(InvalidParameterError, match=match, err_msg=err_msg):
  if any(
  isinstance(X_type, str) and X_type.endswith("labels")
@@ -4315,6 +4321,16 @@ def check_param_validation(name, estimator_orig):
  # the method is not accessible with the current set of parameters
  continue
 
+ err_msg = (
+ f"{name} does not raise an informative error message when the "
+ f"parameter {param_name} does not have a valid value.\n"
+ "Constraints should be disjoint. For instance "
+ "[StrOptions({'a_string'}), str] is not a acceptable set of "
+ "constraint because generating an invalid string for the first "
+ "constraint will always produce a valid string for the second "
+ "constraint."
+ )
+
  with raises(InvalidParameterError, match=match, err_msg=err_msg):
  if any(
  X_type.endswith("labels")