std::vector<char> out;
  TF_EXPECT_OK(ReadCache(&cache1, want_filename, want_offset, want_n, &out));
  EXPECT_EQ(calls, 1);
  TF_EXPECT_OK(ReadCache(&cache2, want_filename, want_offset, want_n, &out));
  EXPECT_EQ(calls, 2);
  TF_EXPECT_OK(ReadCache(&cache3, want_filename, want_offset, want_n, &out));
  EXPECT_EQ(calls, 3);
  TF_EXPECT_OK(ReadCache(&cache4, want_filename, want_offset, want_n, &out));
  EXPECT_EQ(calls, 4);
}