test_unreachable_accuracy can be reached on aarch64

https://cloud.drone.io/conda-forge/scikit-learn-feedstock/44/2/2

__________________________ test_unreachable_accuracy ___________________________
[gw6] linux -- Python 3.7.3 $PREFIX/bin/python

    def test_unreachable_accuracy():
        assert_array_almost_equal(
            orthogonal_mp(X, y, tol=0),
            orthogonal_mp(X, y, n_nonzero_coefs=n_features))
    
        assert_array_almost_equal(
            assert_warns(RuntimeWarning, orthogonal_mp, X, y, tol=0,
>                        precompute=True),
            orthogonal_mp(X, y, precompute=True,
                          n_nonzero_coefs=n_features))

../_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold/lib/python3.7/site-packages/sklearn/linear_model/tests/test_omp.py:79: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

warning_class = <class 'RuntimeWarning'>
func = <function orthogonal_mp at 0xffff965950d0>
args = (array([[ 2.91575919e+00,  1.14685480e+00,  1.81414114e+00,
         3.47278472e+00,  3.69900930e+00, -1.89437288e+00,...   0.06811033],
       [  2.63341917,   0.14703522,   1.76173811],
       [  2.03115852,  -3.98034558,  -6.03227139]]))
kw = {'precompute': True, 'tol': 0}, w = []
result = array([[ 0.        ,  0.        ,  0.        ],
       [ 0.        ,  0.        ,  0.        ],
       [ 0.        ,  ...       ,  0.        ],
       [ 0.        ,  0.        ,  0.        ],
       [ 0.        ,  0.        ,  0.        ]])

    def assert_warns(warning_class, func, *args, **kw):
        """Test that a certain warning occurs.
    
        Parameters
        ----------
        warning_class : the warning class
            The class to test for, e.g. UserWarning.
    
        func : callable
            Callable object to trigger warnings.
    
        *args : the positional arguments to `func`.
    
        **kw : the keyword arguments to `func`
    
        Returns
        -------
    
        result : the return value of `func`
    
        """
        with warnings.catch_warnings(record=True) as w:
            # Cause all warnings to always be triggered.
            warnings.simplefilter("always")
            # Trigger a warning.
            result = func(*args, **kw)
            if hasattr(np, 'FutureWarning'):
                # Filter out numpy-specific warnings in numpy >= 1.9
                w = [e for e in w
                     if e.category is not np.VisibleDeprecationWarning]
    
            # Verify some things
            if not len(w) > 0:
                raise AssertionError("No warning raised when calling %s"
>                                    % func.__name__)
E               AssertionError: No warning raised when calling orthogonal_mp

../_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold/lib/python3.7/site-packages/sklearn/utils/_testing.py:133: AssertionError

Start with sklearn/linear_model/tests/test_omp.py, especially test_unreachable_accuracy around line 79, and reproduce the failure on aarch64. Read the orthogonal_mp call path and the assert_warns helper shown in the traceback. Done means the test's expected RuntimeWarning behavior is consistent and the test passes on aarch64.