In case of doing simple API tests like locking the view or checking properties of objects with known dbId, etc, you can do that on any of the Autodesk storage websites like A360.
You just have to open the model you are interested in, open up the browser console, and there you can access the viewer stored under the NOP_VIEWER variable.
This way you have full access to the viewer, so you can check its properties, and run its functions as shown in the above image.