code: def ref_flip(x, axes):
      if axes is None:
          axes = [len(x.shape) - 1]
      # x = x.copy()
      # for axis in axes:
      #     if axis == 0:
      #         x = x[::-1]
      #     elif axis == 1:
      #         x = x[::, ::-1]
      #     elif axis == 2:
      #         x = x[::, ::, ::-1]
      #     else:
      #         raise
      return np.flip(x, axes)
  
imports: import pytest
  import numpy
  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_flip(x, axes) and returns: np