// block's timestamp to see if it should evict any files. At the current fake
  // timestamp of `now` + 2, file "a" is stale because its first block is stale,
  // but file "b" is not stale yet. Thus, once the pruning thread wakes up (in
  // one second of wall time), it should remove "a" and leave "b" alone.
  uint64 start = Env::Default()->NowSeconds();
  do {
    Env::Default()->SleepForMicroseconds(100000);

  status = env_->GetChildren(dirpath, &children);
  EXPECT_PRED2(UnimplementedOrReturnsCode, status, Code::OK);
  if (!status.ok()) GTEST_SKIP() << "GetChildren() not supported: " << status;

  // All entries must show up in the vector.
  // Must contain only the last name in filenames and dirnames.
  const std::vector<std::string> expected_children = {"a_file", "another_file",