TEST_F(AsStringGraphTest, FillWithChar1) {
  TF_ASSERT_OK(Init(DT_INT64, /*fill=*/"-", /*width=*/4));

  AddInputFromArray<int64>(TensorShape({3}), {-42, 0, 42});
  TF_ASSERT_OK(RunOpKernel());
  Tensor expected(allocator(), DT_STRING, TensorShape({3}));
  test::FillValues<tstring>(&expected, {"-42 ", "0   ", "42  "});
  test::ExpectTensorEqual<tstring>(expected, *GetOutput(0));
}
The software uses a function that accepts a format string as an argument, but the format string originates from an external source.