code: def testNonDtensorVariable(self):
      non_dtensor_variable = variables.Variable(1.0)
      with ops.device_v2(api.device_name()):
          with self.assertRaisesRegex(
              errors_impl.InvalidArgumentError,
              "No default mesh has been registered to DTensor",
          ):
              non_dtensor_variable.read_value()
  
imports: import numpy
  from tensorflow.dtensor.python import api
  from tensorflow.dtensor.python import d_variable
  from tensorflow.dtensor.python import layout
  from tensorflow.dtensor.python.tests import test_util
  from tensorflow.python.eager.polymorphic_function import polymorphic_function
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import errors_impl
  from tensorflow.python.framework import ops
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import array_ops_stack
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import variables
  from tensorflow.python.platform import test
label_desc: Use image node_id 2 for calling the DTensorVariableTest obj's underlying member method code with example usage: obj.testNonDtensorVariable() without return types