Client test is a, more or less, complete bittorrent client. It lacks most settings and you can't start or stop torrents once you've started it. All the settings are hard coded. The command line arguments are:
client_test <filename1.torrent> <filename2.torrent> ...
You can start any number of torrent downloads/seeds via the command line. If one argument starts with http:// it is interpreted as a tracker announce url, and it expects an info-hash as the next argument. The info-hash has to be hex-encoded. For example: 2410d4554d5ed856d69f426c38791673c59f4418. If you pass an announce url and info-hash, a torrent-less download is started. It relies on that at least one peer on the tracker is running a libtorrent based client and has the metadata (.torrent file). The metadata extension in libtorrent will then download it from that peer (or from those peers if more than one).
While running, the client_test sample will look something like this:
The commands available in the client are:
The list at the bottom (shown if you press d) shows which blocks has been requested from which peer. The green background means that it has been downloaded. It shows that fast peers will prefer to request whole pieces instead of downloading parts of pieces. It may make it easier to determine which peer that sent the corrupt data if a piece fails the hash test.