Classes are being created without packages in Netbeans
Solution 1:
Not sure if I understood the question correctly, but if your problem is, that the DesctopLauncher doesn't know the class Testo you just need to import it: import com.supa.testa.Testo
Also you should place your Game classes (and packages) like Testo in the core project, since it will be used in all projects (desctop and ios).
You should have a look at the libGDX tutorials.
Especially Setup and Hello World should contain what you are searching for.