code: def test_watershed_4():
      myfield = basic_field_3()
      idx, label = myfield.custom_watershed()
      assert np.size(idx) == 9
      assert (
          np.unique(
              [
                  label[555],
                  label[0],
                  label[9],
                  label[90],
                  label[99],
                  label[900],
                  label[909],
                  label[990],
                  label[999],
              ]
          ).size
          == 9
      )
  
imports: import numpy
  import numpy.random
  from numpy.testing import assert_array_equal
  from ..field import field_from_coo_matrix_and_data, field_from_graph_and_data
  from ..graph import wgraph_from_3d_grid
label_desc: Use image node_id 19 for calling a global function with example usage: test_watershed_4() without return types