code: def test_dtypes(self, dtype_i, dtype_o):
      x = testing.shaped_arange((2, 3, 4, 5), dtype=dtype_i)
      if numpy.can_cast(dtype_o, x.dtype):
  
          def func(x):
              return x
  
          gufunc = _GUFunc(func, "(i,j)->(i,j)")
          z = gufunc(x, dtype=dtype_o)
          assert z.dtype == dtype_o
          testing.assert_allclose(z, x)
  
imports: import numpy
  import pytest
  import cupy
  from cupy import testing
  from cupy._core._gufuncs import _GUFunc
label_desc: Use image node_id 1 for calling the TestGUFuncDtype obj's underlying member method code with example usage: obj.test_dtypes(dtype_i, dtype_o) and returns: x