code: def test_empty(self):
      A, B, C, D = self.data()
  
      expected = cupy.empty((0, 0), dtype=self.dtype)
      testing.assert_array_equal(
          _construct.bmat([[None, None]]).todense(), expected
      )
      testing.assert_array_equal(
          _construct.bmat([[None, D], [D, None]]).todense(), expected
      )
  
imports: import functools
  import re
  from unittest import mock
  import numpy
  import pytest
  import cupy
  from cupy import testing
  from cupy.cuda import runtime
  from cupyx.scipy import sparse
  from cupyx.scipy.sparse import _construct
label_desc: Use image node_id 3 for calling the TestBmat obj's underlying member method code with example usage: obj.test_empty() without return types