svoid test_BackupThinner() {
  new BackupThinner bt;
  var f2 = newFile("concepts.structure.gz.backup20240518-19");
  bt.allFiles(ll(
    newFile("concepts.structure.gz.backup20240518-21"),
    f2,
    newFile("concepts.structure.gz.backup20240401-10")));
  bt.timeZone(germanTimeZone());
  
  bt.currentTime(timestampFromYMDHM(2024, 5, 18, 22, 0, bt.timeZone()));
  bt.scan();
  assertEmpty(bt.deletableFiles);
  
  bt.currentTime(timestampFromYMDHM(2025, 5, 18, 22, 0, bt.timeZone()));
  bt.scan();
  assertListEquals(ll(f2), bt.deletableFiles);
}