code: def _check(self, backend_config):
      mask = self.mask if self.specify_mask else None
      x, mask = backend_config.get_array((self.x, mask))
      with chainer.using_config("train", self.train), backend_config:
          out, out_mask = functions.dropout(
              x, 0.5, mask=mask, return_mask=True
          )
  
      if self.train:
          assert isinstance(out_mask, type(out.array))
          if mask is None:
              assert out_mask.shape == out.array.shape
          else:
              assert out_mask is mask
      else:
          assert out_mask is None
  
      with chainer.using_config("train", self.train):
          out2 = functions.dropout(
              self.x, 0.5, mask=cuda.to_cpu(out_mask)
          )
      testing.assert_allclose(out.array, out2.array)
  
imports: import unittest
  import numpy
  import chainer
  from chainer.backends import cuda
  from chainer import functions
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 2 for calling the TestDropoutMask obj's underlying member method code with example usage: obj._check(backend_config) without return types