Run tests with multiple devices

This page helps you use the Trade Federation Test Harness with multiple devices during testing.You should first become familiar with normal usage as described in the end-to-end example.

What is different with multiple devices?

Several things are different when configuring and running multi-device tests in Trade Federation, in particular:

Any existing one-device configuration is valid for multi-device mode.

<! -- TODO: Clarify the sentence immediately above by adding an example of a one-device use case as it pertains to multi-device mode in a second sentence. -->>

Multiple device configuration

This document assumes you are already familiar with the typical TF test configuration. Here is what a typical test configuration with two devices looks like:

<configuration description="A simple multi-devices example in Tradefed">

    <device name="device1">
        <target_preparer class="" />

    <device name="device2">
        <target_preparer class="" />

    <option name="log-level" value="verbose" />
    <test class="" />

    <logger class="" />
    <result_reporter class="" />


Several things need to be mentioned about the structure:

  • For each device that will be needed, a <device> is expected.
  • <build_provider>, <target_preparer>, <device_recovery>, <device_requirements>, and <device_options> if needed must be included within the <device> tag; an exception will be thrown otherwise.
  • the name attribute for <device> is mandatory and should be unique among all the devices present in the configuration. It is used to reference the particular device associated with it. This allows your test to target a particular device.
  • <option> can have either a global scope when at the root of the configuration or be limited to device scope when specified inside the <device> tag.

All other rules applicable to single-device configuration are still applicable here. See the Hello World example below for more details.

Command line update

When specifying options on the TF command line, it is also possible to specify a device scope using {<device name>} where <device name> is the name specified in the XML configuration.

In the example above, the following options were allowed:

  • --device-setup:disable

You may target only one of the device build_provider objects using the device name, like so:


In this example, device2 skips the device setup while device1 doesn't.

How does TF select the devices?

Trade Federation looks for a device matching the device_requirements (typically the device flavor, product, etc.) in order of device appearance in the configuration. Each time a device is allocated, TF tries to allocate the next one. If it is not possible to allocate all of the devices, they will all be released and the command will be re-attempted when all devices are matched.

How does TF prepare the devices?

The preparation step for multi-devices is mostly the same as for single devices. Each device is prepared by calling the <target_preparer> in order of appearance inside the <device>.

You may also use <multi_target_preparer> specified at the root of the configuration that enables preparation steps requiring multiple devices, such as pairing of devices. It runs after the target_preparer step.

An alternative is <pre_multi_target_preparer> that runs before the target_preparer step.

  • <pre_multi_target_preparer> should be used for setup that must be done before individual device setup.
  • <multi_target_preparer> should be used for setup that must be done after individual device setups.

For example:

flash device 1 (target_preparer) flash device 2 (target_preparer) bluetooth connect both devices (multi_target_preparer)

Write a multi-device test

When writing a regular single-device test, you implement the IDeviceTest interface.

For the tests to receive the devices under test, you can implement either IMultiDeviceTest or IInvocationContextReceiver.

IMultiDeviceTest gives you a direct map of device to its IBuildInfo while IInvocationContextReceiver later gives you the complete context (device, IBuildInfo & metadata).

You will then be able to use the usual ITestDevice APIs that TF put at disposition for test writing.

No APIs yet exist to conduct operations from one device to another, such as device1.sync(device2). If you think you have a compeling use case to be supported, send your reasoning to the android-platform list.

Multi devices hello world example

We added a Hello World-like example configuration: multi-devices.xml There is also an example of multi_target_preparer implementation HelloWorldMultiTargetPreparer that shows how to receive the list of devices and their builds.

This is a full example that involves:

  • Allocating two devices
  • Accessing both devices through a multi_target_preparer
  • Running a test that use the two devices

Once you have built Tradefed, you can use the following command in TF shell:

run example/multi-devices

You should see some output containing the following:

08-15 10:52:43 I/HelloWorldMultiDevices: Hello World! device '00b4e73b4cbcd162' with build id '3146108'
08-15 10:52:43 I/HelloWorldMultiDevices: Hello World! device 'LP5A390056' with build id '3146108'
08-15 10:52:43 I/HelloWorldMultiDevices: Hello World! device '00b4e73b4cbcd162' from context with build ''
08-15 10:52:43 I/HelloWorldMultiDevices: Hello World! device 'LP5A390056' from context with build ''

You need two devices connected in order to run the above. This can be checked via: adb devices

When the invocation is in progress, you can monitor it like single devices with list i and list d:

tf >list i
Command Id  Exec Time  Device                          State
1           0m:35      [00b4e73b4cbcd162, LP5A390056]  fetching build
tf >list d
Serial            State      Product   Variant   Build   Battery
00b4e73b4cbcd162  Allocated  bullhead  bullhead  NRD90O  100
LP5A390056        Allocated  shamu     shamu     NRD90I  100

You should be able to see the devices involved in each invocation, as well as all of the available devices and their respective state.

Note that in this example we called the two devices in the configuration device1 and device2; you should give a more descriptive name if possible depending on the type of device you are really expecting to be set.