import pytest

from landlab import RasterModelGrid
from landlab.components import DrainageDensity, FlowAccumulator

def test_route_to_multiple_error_raised():
    mg = RasterModelGrid((10, 10))
    z = mg.add_zeros('node', 'topographic__elevation')
    z += mg.x_of_node + mg.y_of_node
    fa = FlowAccumulator(mg, flow_director='MFD')
    fa.run_one_step()

    channel__mask = mg.zeros(at='node')

    with pytest.raises(NotImplementedError):
        DrainageDensity(mg, channel__mask=channel__mask)
