To test your build, you can either run your build on an emulator or run (flash) it on an actual device.
Test your build on an emulator
Cuttlefish is a virtual device emulator used to test your builds. For information on running a build on Cuttlefish, see Get started guide.
For app testing, including Google Automotive Services (GAS) apps, use Android Emulator.
Test your build on a device
The fastboot tool lets you to flash more device types than the Android Flash Tool and can be use to flash your own local builds to devices for testing.
For information on using the fastboot command-line tool, see Flash with Fastboot