Key key = std::make_pair(filename, pos);
    // Look up the block, fetching and inserting it if necessary, and update the
    // LRU iterator for the key and block.
    std::shared_ptr<Block> block = Lookup(key);
    if (!block) {
      std::cerr << "No block for key " << key.first << "@" << key.second;
      abort();
    }
    MaybeFetch(key, block, status);

  env->SetNowSeconds(3);
  int value = 0;
  EXPECT_TRUE(cache.Lookup(key, &value));
  EXPECT_EQ(value, 42);
  // 2 seconds after the most recent insertion, the entry is no longer valid.
  env->SetNowSeconds(4);
  EXPECT_FALSE(cache.Lookup(key, &value));
  // Re-insert the entry.
  cache.Insert(key, 43);
  EXPECT_TRUE(cache.Lookup(key, &value));
  EXPECT_EQ(value, 43);
  // The entry is valid 1 second after the insertion...

  //  Worker1:
  //  cluster { job { name: "client" tasks { key: 0 value: "localhost:14525" } }
  //            job { name: "worker" tasks { key: 1 value: "localhost:14523" } }
  //          } job_name: "worker" task_index: 1 protocol: "grpc"
  //
  //  Worker0:
  //  cluster { job { name: "client" tasks { key: 0 value: "localhost:14526" } }
  //            job { name: "worker" tasks { key: 0 value: "localhost:14522" } }