code: def test_gcn_filter():
      t = tr.GCNFilter()
      assert callable(t)
      g = Graph(x=x, a=a, e=e, y=y_nl)
      t(g)
      g = Graph(x=x, a=a.A, e=e, y=y_nl)
      t(g)
  
file_path: spektral/tests/test_transforms/test_transforms.py
imports: import numpy
  import scipy.sparse
  from spektral import transforms
  from spektral.data import Graph
label_desc: Use image node_id 6 for calling a global function with example usage: test_gcn_filter() without return types