Actually, you can do this if you have Android Studio installed. I use it for testing the Texting component. It requires a bit of a dance but here is what you can do:
- Create two Android Virtual Devices (AVDs) in Android Studio. Use the x86_64 image if you're on an x86_64 architecture or arm64 if on an ARM device.
- Launch the two emulators and drag the App Inventor companion app APK onto the emulator window to install the app.
- Note that the two emulators run on different ports. The first one will be port 5554 and the second will be 5556. You will want to stop the one that is 5554.
- Use the Connect > Emulator option in App Inventor to establish a connection to the second emulator.
- Once the app shows in the emulator, reload the App Inventor window to get a fresh session.
- Start the first emulator (5554) again.
- Use the Connect > Emulator option in App Inventor to establish a connection to the first emulator.
- Send messages between the two emulators using their port numbers as the phone numbers (5554 and 5556 for emulator 1 and 2, respectively).