To test on physical devices, connect two devices locally and enable USB debugging setting on both devices.
When running on a cloudtop or other remote setups, use pontis to connect the devices on remote set up by running pontis start. Verify that pontis client is connected via pontis status and confirm that both devices are in "connected" state via adb devices.
See go/pontis for more details regarding this workflow.
To test on virtual devices, follow instructions to set up netsim on cuttlefish. Launch two instances of virtual devices by specifying --num_instances=2 parameter.
atest CompanionDeviceManagerMultiDeviceTestCases