code: def test_flatten_order(self, xp, order):
      a = testing.shaped_arange((2, 3, 4), xp)
      return a.flatten(order)
  
imports: import numpy
  import pytest
  import cupy
  from cupy import testing
  from cupy import _util
label_desc: Use image node_id 4 for calling the TestArrayFlatten obj's underlying member method code with example usage: obj.test_flatten_order(xp, order) and returns: a