code: def ref_concatenate(*inputs, **params):
      axis = params.pop("axis", len(inputs[0].shape) - 1)
      return np.concatenate(inputs, axis=axis)
  
file_path: nnabla/python/test/function/test_concatenate.py
imports: import pytest
  import numpy
  import nnabla
  import nnabla.functions
  from nbla_test_utils import list_context
label_desc: Use image node_id 1 for calling a global function with example usage: ref_concatenate() and returns: np