I am using the Test Pattern Generator in constant mode in v6.0 of the core.
However, when I update to v7.0 in Vivado 2015.3, I can no longer disable the AXI Lite interface and I do not see video coming out of the core when I leave it unconnected.
The Test Pattern Generator no longer supports constant mode starting in v7.0.
You must write some registers via AXI Lite to configure and enable the IP.
Refer to the IP and driver documentation for more information.