code: def ref_clip_by_norm(x, clip_norm, axis):
      x_norm = np.sqrt(np.sum(x**2.0, axis=axis, keepdims=True))
      x = clip_norm * x / np.maximum(x_norm, clip_norm)
      return x
  
file_path: nnabla/python/test/function/test_clip_by_norm.py
imports: import pytest
  import numpy
  import nnabla
  import nnabla.functions
  from nbla_test_utils import list_context
  from nnabla.testing import assert_allclose
label_desc: Use image node_id 1 for calling a global function with example usage: ref_clip_by_norm(x, clip_norm, axis) and returns: x