code: def test_spring_init_pos(self):
      # Tests GH #2448
      import math
  
      G = nx.Graph()
      G.add_edges_from([(0, 1), (1, 2), (2, 0), (2, 3)])
  
      init_pos = {0: (0.0, 0.0)}
      fixed_pos = [0]
      pos = nx.fruchterman_reingold_layout(
          G, pos=init_pos, fixed=fixed_pos
      )
      has_nan = any(
          math.isnan(c) for coords in pos.values() for c in coords
      )
      assert not has_nan, "values should not be nan"
  
imports: import pytest
  import networkx
label_desc: Use image node_id 3 for calling the TestLayout obj's underlying member method code with example usage: obj.test_spring_init_pos() without return types