The official interactive map is updated with all the landmarks/treasures/enemy pins and you can see it in the image above (or click on the link if you want to see the interactive map itself).
5 Treasure Chests in Old Weapon Testing Ground
1. Beside the Aether’s Wars Terminal (can be seen by the icon on the map).
2. On the top platform facing the arena. If you haven’t already, there is a hidden achievement ‘First Things First’ involving a Mysterious Stranger near this spot.
3. Down the stairs from previous platforms. You can get a hidden achievement ‘Confession of the Mask’ in this exact spot after completing a certain task.
5. Go to the lift to the bottom floor (huge arena) and go to the right side of the arena.