code: def test_unroll_none_input_error():
      # Test that a ValueError is raised if unroll scan is True and the input
      # sequence length is specified as None.
      l_in = InputLayer((2, None, 3))
      with pytest.raises(ValueError):
          RecurrentLayer(l_in, 5, unroll_scan=True)
  
      with pytest.raises(ValueError):
          LSTMLayer(l_in, 5, unroll_scan=True)
  
      with pytest.raises(ValueError):
          GRULayer(l_in, 5, unroll_scan=True)
  
imports: import pytest
  from lasagne.layers import RecurrentLayer, LSTMLayer, CustomRecurrentLayer
  from lasagne.layers import InputLayer, DenseLayer, GRULayer, Gate, Layer
  from lasagne.layers import helper
  import theano
  import theano.tensor
  import numpy
  import lasagne
  from mock import Mock
label_desc: Use image node_id 56 for calling a global function with example usage: test_unroll_none_input_error() without return types