code: def testUnnest_NonExistingKey(self):
      [x1, x2, x3] = self.create_artifacts(uri_prefix="x/", n=3)
      input_dict = {"x": [x1, x2, x3]}
  
      with self.assertRaisesRegex(
          exceptions.FailedPreconditionError,
          "Input dict does not contain the key y.",
      ):
          self._unnest(input_dict, key="y")
  
file_path: tfx/tfx/dsl/input_resolution/ops/unnest_op_test.py
imports: import tensorflow
  from tfx.dsl.input_resolution import resolver_function
  from tfx.dsl.input_resolution import resolver_op
  from tfx.dsl.input_resolution.ops import ops
  from tfx.dsl.input_resolution.ops import test_utils
  from tfx.orchestration.portable.input_resolution import exceptions
label_desc: Use image node_id 6 for calling the UnnestOpTest obj's underlying member method code with example usage: obj.testUnnest_NonExistingKey() without return types