return ToOperation(iter->second);
  }
}

TF_Operation* TF_GraphNextOperation(TF_Graph* graph, size_t* pos) {
  if (*pos == 0) {
    // Advance past the first sentinel nodes in every graph (the source & sink).
    *pos += 2;
  } else {
    // Advance to the next node.
    *pos += 1;
  }

  mutex_lock l(graph->mu);
  while (*pos < static_cast<size_t>(graph->graph.num_node_ids())) {

  // `modular_filesystem_test.h` and extend the instantiation to also take as
  // argument an implementation for this method/a subclass factory (see
  // https://github.com/google/googletest/blob/master/googletest/docs/advanced.md#creating-value-parameterized-abstract-tests)
  std::string GetURIForPath(StringPiece path) {
    const std::string translated_name =
        tensorflow::io::JoinPath(root_dir_, path);

      [&env]() { return env->NowSeconds(); });
  // Execute the first read to load the block.
  TF_EXPECT_OK(ReadCache(&cache1, "", 0, 1, &out));
  EXPECT_EQ(calls, 1);
  // Now advance the clock one second at a time and redo the read. The call
  // count should advance every 3 seconds (i.e. every time the staleness is
  // greater than 2).
  for (int i = 1; i <= 10; i++) {
    env->SetNowSeconds(i + 1);