https://www.youtube.com/watch?v=PpbSnfKZg5wI watched this video a while ago, and in addition to this, most times I pass the Craigieburn Maintenance centre, there is an X'trapolis there. For those who cannot be bothered watching the video, it is of an X'trapolis train on the Sunbury line at Keilor Plains [edit: I haven't used the link feature before, so sorry for stating the bleeding obvious!]. I'm assuming that they were just testing that day, but why? And as for Craigieburn, they must be performing some form of maintenance, or do they just need the stabling? It would be interesting seeing them move from Craigieburn when they do. Anyway, I'm hoping this thread can not only answer my questions but also serve as some sort of a discussion point for future sightings.