def METHOD_NAME():
    mg = RasterModelGrid((10, 10))
    mg.add_zeros("topographic__elevation", at="node")
    noise = np.random.rand(mg.size("node"))
    mg.at_node["topographic__elevation"] += noise
    fr = FlowAccumulator(mg, flow_director="D8")
    fr.run_one_step()
    with pytest.raises(ValueError):
        DrainageDensity(
            mg,
            area_coefficient=1,
            slope_coefficient=1,
            area_exponent=1,
            slope_exponent=1,
        )