def test_b_ffill_use_bottleneck_numbagg(method, compute_backend):
    """
    bfill & ffill fail if both bottleneck and numba are disabled
    """
    da = xr.DataArray(np.array([4, 5, np.nan], dtype=np.float64), dims="x")
    with pytest.raises(RuntimeError):
        getattr(da, method)("x")

    bfill & ffill fail if both bottleneck and numba are disabled
    
xarray/tests/test_missing.py