code: def test_vstack_dtype(self, xp, dtype1, dtype2):
      a = testing.shaped_arange((3, 4), xp, dtype1)
      b = testing.shaped_arange((3, 4), xp, dtype1)
      return xp.vstack((a, b), dtype=dtype2)
  
imports: import numpy
  import pytest
  import cupy
  from cupy import testing
  from cupy import cuda
label_desc: Use image node_id 41 for calling the TestJoin obj's underlying member method code with example usage: obj.test_vstack_dtype(xp, dtype1, dtype2) and returns: xp