This video was hosted on Vidme, which is no longer in operation. However, you might find this video at one of these links:
Warp test for PET and PETG filament
August 8 2015
Because of the very low warpage of PET filament, this print is designed to warp very easily so the printer can be tested. http://www.thingiverse.com/thing:990484 The base is thin so will flex upwards easily. The design is long, giving lots of room for warp to occur. The pointy ends provide almost no attachment to the bed, yet easily show any warpage upwards. The bottom corners are square (the worst kind for warps). The tall rails give lots of leverage for the top layers to contract.