code: def testEvaluateNoneExistentTensorGeneratesError(self):
      dump = test.mock.MagicMock()
  
      def fake_get_tensors(
          node_name, output_slot, debug_op, device_name=None
      ):
          del node_name, output_slot, debug_op, device_name  # Unused.
          raise debug_data.WatchKeyDoesNotExistInDebugDumpDirError()
  
      with test.mock.patch.object(
          dump, "get_tensors", side_effect=fake_get_tensors
      ):
          ev = evaluator.ExpressionEvaluator(dump)
          with self.assertRaisesRegex(
              ValueError,
              "Eval failed due to the value of .* being unavailable",
          ):
              ev.evaluate("np.matmul(`a:0`, `b:0`)")
  
imports: import numpy
  from tensorflow.python.debug.cli import evaluator
  from tensorflow.python.debug.lib import debug_data
  from tensorflow.python.framework import test_util
  from tensorflow.python.platform import test
label_desc: Use image node_id 3 for calling the EvaluatorTest obj's underlying member method code with example usage: obj.testEvaluateNoneExistentTensorGeneratesError() without return types