I have a couple of questions about how you guys approach testing for performance. For example, lets say my constraints are that my app needs to work on mobile and desktop and needs to support 4 year old laptops and 3 years old mobile devices. Does Babylon offer some tools to test performance or do you guys use other tools? For testing to makes sure that your app still runs well on older devices, what tools do you use for that?
We do offer the all mighty Inspector 
(scene.debugLayer.show()) which provides a lot of insights information.
Then I would simply recommend using the F12 profiler to find any bottlenecks
And if you are REALLY into optimizations: https://spector.babylonjs.com/
Thanks for the information! This might not be really a Babylon specific question, but how do you usually test on older devices that has less performance than your current laptop or mobile phone?
If you have example hardware, then you just try it on one. Otherwise, profiling & optimizing is all you can really do.
After all, there is not just on type of 4 year old laptop. Unless, you really scale back your objectives, you cannot really do a good job on a machine without a gpu. A real cut rate machine with “integrated graphic” aka “no gpu” could have been manufactured yesterday.