message: Update test to use tensorflow::tstring.
diff: @@ -61,7 +61,7 @@ std::vector<Tensor> tensor_doubles{
  test::AsTensor<double>({400.0}), test::AsTensor<double>({800.0})};
  const string str = "test string"; // NOLINT
  -std::vector<Tensor> tensor_strs{test::AsTensor<string>({str})};
  +std::vector<Tensor> tensor_strs{test::AsTensor<tstring>({str})};
  const DatasetTestParam test_cases[] = {
  {_int32, tensor_int32s, 4 /*bytes*/ * 9 /*elements*/},
  