new_contents: import numpy as np
  from numpy.testing import assert_allclose
  
  from geonet.flow import find_arc_flow
  from geonet.geometry import star_angles
  from geonet.mintrans import steiner_pos
  from geonet.network import SteinerTree
  
  
  
  def test_length():
      '''check Steiner tree geometric property for minimized length'''
      nodes = 'abcs'
      arcs = ['as', 'bs', 'cs']
      terminals = {'a': (0,0), 'b': (1,0), 'c': (0,1)}
      tree = SteinerTree(nodes, arcs, terminals)
  
      flow = find_arc_flow(tree, {'a':-4, 'b':2, 'c':2})
  
      pos = steiner_pos(tree, flow, flow_exp=0.0)
  
      # check that fixed positions are kept
      for k,v in terminals.items():
          assert_allclose(pos[k], v, atol=1e-7)
  
      # check (known) optimal position
      assert_allclose(pos['s'], (0.211, 0.211), atol=1e-3)
  
      # check angle property of Steiner node position
      # all angles are equal (to 120 deg = 2/3 pi)
      angles = star_angles('s', 'abc', pos)
      assert_allclose(angles, [2.0/3.0*np.pi]*3, atol=1e-4)
  
subject: add test for mintrans