code: def test_layer_preprocess():
      from spektral.layers import GCNConv
  
      t = tr.LayerPreprocess(GCNConv)
      assert callable(t)
      g = Graph(x=x, 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 8 for calling a global function with example usage: test_layer_preprocess() without return types