Last I heard, these trains are intended for the Piccadilly, Bakerloo, Central and W&C. They are only going to the Piccadilly first because of its status as an Airport Link.
Bit of an unfair test. That track is just one long loop, no super curvy bits in succession, and it's squeaky clean and perfectly level. Will be a whole different ball game when it's on the actual Piccadilly line tracks!
It's a track which features two kinds of third rail, top contact which the train is using, and bottom contact, which is less commonly used, but looks like the kind of third rail used by the Berlin S-Bahn, likely for the testing of the Class 483 which was jointly built by Siemens and Stadler (Stadler has a factory in Berlin). Fourth Rail is likely too unusual to add to the test track for, especially if the trains can easily be adjusted to work between Fourth Rail and also 750V top contact third rail, which is common at least in parts of London.
