code: def test_external_mean_zero_len(self, xp, dtype):
      shape, axis = self.params
      a = testing.shaped_arange(shape, xp, dtype)
      f = getattr(xp, self.func)
      return f(a, axis=axis)
  
imports: import math
  import numpy
  import pytest
  import cupy
  from cupy import testing
label_desc: Use image node_id 1 for calling the TestProductZeroLength obj's underlying member method code with example usage: obj.test_external_mean_zero_len(xp, dtype) and returns: f