Input power requirements for "load regulation" tests on DC power supplies
While there are no standards, the range of parameters you test will depend on the type of testing you are doing:

Manufacturing test; here you would certainyl want to span the characteristics that give you the best possiblity of finding early failure devices. 


Test the full spectrum of Vin at full load
Test startup and settle times for maximum and minimum loads at Vin minimum
Some soak test (probably lowest Vin and max load) to find early failures (this could be minutes to hours depnding on the supply). It might also include IR monitoring for hotspots.


Inbound test; here you are expecting the manufacturer to have already performed a broad scale test and you want just to detect failed units as a sanity check.


Startup settle at full load and minimal Vin
Multiple power cycle at min and max load