Ashok, possibly since the time whn the question has been asked you have been turned into GIS testing expert, but let me try to answer )))
I would focus on what the app should do with geometries:
does it takes into account the correct type of geometries, does it ignore the incorrect ones
If the app builds own geometries based on the original geometries, I would try different topologies that may be problematic for doing this. Say, the app should draw a geometry 5 px left to some original geometry, in parallel to it. I would try a loop that is lesser than 10 px diameter in order to have no space to 5 px left. And so on
I would test the huge values of data, so what will be if the app would try to consume the worldwide net of such geometries.