old_contents: import pytest
  
  from chainerx import _cuda
  
  
  try:
      import cupy
  except Exception:
      cupy = None
  
  
  class CupyTestMemoryHook(cupy.cuda.memory_hook.MemoryHook):
  
      name = 'CupyTestMemoryHook'
  
      def __init__(self):
          self.used_bytes = 0
          self.acquired_bytes = 0
  
      def alloc_preprocess(self, **kwargs):
          self.acquired_bytes += kwargs['mem_size']
  
      def malloc_preprocess(self, **kwargs):
          self.used_bytes += kwargs['mem_size']
  
  
  @pytest.mark.cuda()
  def test_cupy_share_allocator():
      with CupyTestMemoryHook() as hook:
          cp_allocated = cupy.arange(10)
  
          used_bytes = hook.used_bytes
          acquired_bytes = hook.acquired_bytes
  
          # Create a new array after changing the allocator to the memory pool
          # of ChainerX and make sure that no additional memory has been
          # allocated by CuPy.
  
          _cuda.cupy_share_allocator()
  
          chx_allocated = cupy.arange(10)
  
          cupy.testing.assert_array_equal(cp_allocated, chx_allocated)
  
          assert used_bytes == hook.used_bytes
          assert acquired_bytes == hook.acquired_bytes
  
new_contents: import pytest
  
  from chainerx import _cuda
  
  
  try:
      import cupy
  except Exception:
      cupy = None
  
  
  class CupyTestMemoryHook(cupy.cuda.memory_hook.MemoryHook):
  
      name = 'CupyTestMemoryHook'
  
      def __init__(self):
          self.used_bytes = 0
          self.acquired_bytes = 0
  
      def alloc_preprocess(self, **kwargs):
          self.acquired_bytes += kwargs['mem_size']
  
      def malloc_preprocess(self, **kwargs):
          self.used_bytes += kwargs['mem_size']
  
  
  @pytest.mark.cuda()
  def test_cupy_share_allocator():
      with CupyTestMemoryHook() as hook:
          cp_allocated = cupy.arange(10)
  
          used_bytes = hook.used_bytes
          acquired_bytes = hook.acquired_bytes
          assert used_bytes > 0
          assert acquired_bytes > 0
  
          # Create a new array after changing the allocator to the memory pool
          # of ChainerX and make sure that no additional memory has been
          # allocated by CuPy.
  
          _cuda.cupy_share_allocator()
  
          chx_allocated = cupy.arange(10)
  
          cupy.testing.assert_array_equal(cp_allocated, chx_allocated)
  
          assert used_bytes == hook.used_bytes
          assert acquired_bytes == hook.acquired_bytes
  
subject: Add safety checks in test