So I'm currently helping to develop an app and I've been asked to test it on as many devices (virtual/non virtual) as possible and then make it adjust it to as many different screen sizes and even tablets as possible. 

Now I'm not sure where exactly to start because I don't know if Android Virtual Device Manager in Eclipse has every possible screen combination.

So, would setting up and running all of the 21 virtual devices in Eclipse do the job? Or is there something else I should try doing? Any kind of information would be helpful, thank you!