code: def test_watershed_3():
      myfield = basic_field_2()
      myfield.field[555] = 10
      myfield.field[664] = 0
      idx, label = myfield.custom_watershed(0, 11)
      assert np.size(idx) == 8
  
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 21 for calling a global function with example usage: test_watershed_3() without return types