Hi Ludwin,
the best way is to use physical devices.
The best would be to use exactly the device used by the end user, but it is no always possible to do this.
bugs in mobile apps are often device specific :-(
In addition you can try the visual studio emulator for android.
You do not have to use or install visual studio to use this emulator.
Also the emulator should be free.
Older version of the emulator where a little bit buggy and had some problems with appeon mobile apps.
But finally it works ok for our needs.
Regards
Heino