Tast Codelab: Remote tests (go/tast-codelab-4)

This document assumes that you've already gone through Codelab #1.

This codelab follows the creation of a remote Tast test and a gRPC service used by the test.


In Tast our reference point is the DUT, so anything not running on the DUT is considered to be remote in the Tast context. So remote tests are tests which do not run on the DUT itself but on a remote host. They are needed when a test needs to reboot the DUT during the test execution for any reason. Alternatively a remote fixture can be used when reboots are only needed in a preparation step for the test (e.g. enrollment, resetting hardware etc.). The remote host can communicate with the DUT via ssh or gRPC services during the test, which are used to execute code on the DUT itself.

remote test

Unless ssh calls are enough for the test, the remote test will consist of two parts:

  1. The remote part which includes all the initialization steps and calls to gRPC services.
  2. One or more gRPC services which execute the required code on the DUT, e.g. for login, the general test logic and cleaning up the DUT.

gRPC services

The gRPC services are created using protocol buffers to define their signatures, their respective request and response message types. We create a proto file with the definition in the folder in tast-tests/src/chromiumos/tast/services/cros that corresponds to the test. So if you need a service for a policy test the folder used will be policy. In this example we will create a service with a method that checks if the timezone set on the DUT matches a given timezone. So we need one method TestSystemTimezone() which performs the check. The request message type for the method will be TestSystemTimezoneRequest and contains a timezone string. As the method doesn't return anything except for an error when it fails the response message type is google.protobuf.Empty. As option we will also define a go_package of which this service should be part of.

syntax = "proto3";

package tast.cros.policy;

import "google/protobuf/empty.proto";

option go_package = "chromiumos/tast/services/cros/policy";

// SystemTimezoneService provides a function to test the system timezone.
service SystemTimezoneService {
  rpc TestSystemTimezone(TestSystemTimezoneRequest) returns (google.protobuf.Empty) {}

message TestSystemTimezoneRequest {
  string Timezone = 1;

In order to generate the go code for this service we add its proto file to the gen.go file in the same folder.

// Package policy provides the PolicyService
package policy

// Run the following command in CrOS chroot to regenerate protocol buffer bindings:
// ~/trunk/src/platform/tast/tools/go.sh generate chromiumos/tast/services/cros/policy
//go:generate protoc -I . --go_out=plugins=grpc:../../../../.. system_timezone.proto

Then we run ~/trunk/src/platform/tast/tools/go.sh generate chromiumos/tast/services/cros/folder as stated in the gen.go file. This will generate a system_timezone.pb.go file which contains the go code for the service.

NOTE: When committing a remote test with gRPC services, make sure to also submit the generated files.

Local service implementation

Next we need to implement what the TestSystemTimezone method is actually doing on the DUT. The service implementation is placed in the same folder as respective local tests. So again if you are writing a remote policy test, all created services for that test go in the src/chromiumos/tast/local/bundles/cros/policy folder.

For the implementation we need to import the respective package we assigned our service to as well as the grpc package. As we use an empty response in our service we also need the protobuf/ptypes/empty package.

import (

	pb "chromiumos/tast/services/cros/policy"

In the init() function we only add a service instead of a test:

func init() {
		Register: func(srv *grpc.Server, s *testing.ServiceState) {
			pb.RegisterSystemTimezoneServiceServer(srv, &SystemTimezoneService{s: s})

Then we need a struct to hold our service:

// SystemTimezoneService implements tast.cros.policy.SystemTimezoneService.
type SystemTimezoneService struct {
	s *testing.ServiceState

And finally we need an implementation for all methods defined in our service. All methods return their respective response message and an error as second return value which needs to be checked by the caller. In this case this is just the TestSystemTimezone() method which returns a reference to empty.Empty{} and an error if the check fails. These methods are the part of the remote test that get executed on the DUT, so we can put most of our test logic in these:

func (c *SystemTimezoneService) TestSystemTimezone(ctx context.Context, req *pb.TestSystemTimezoneRequest) (*empty.Empty, error) {

	if err := upstart.RestartJob(ctx, "ui"); err != nil {
		return nil, errors.Wrap(err, "failed to log out")

	// Wait until the timezone is set.
	if err := testing.Poll(ctx, func(ctx context.Context) error {

		out, err := os.Readlink("/var/lib/timezone/localtime")
		if err != nil {
			return errors.Wrap(err, "failed to get the timezone")
		outStr := strings.TrimSpace(string(out))

		if !strings.Contains(outStr, req.Timezone) {
			return errors.Errorf("unexpected timezone: got %q; want %q", outStr, req.Timezone)

		return nil

	}, &testing.PollOptions{
		Timeout: 30 * time.Second,
	}); err != nil {
		return nil, err

	return &empty.Empty{}, nil

In this example the TestSystemTimezone() method will poll the currently set timezone on the console and compare it to the timezone in the input parameter. The function always returns a reference to empty.Empty{} as request response and when the timezones don't match until the polling timeout is reached it also returns an error. The error indicates that the timezone on the DUT is not the expected timezone.

The full implementation of the local service can be found here

Remote test

The remote tests themselves are put into their respective folder in tast-tests/src/chromiumos/tast/remote/bundles/cros, so in the case of a policy test they are placed in tast-tests/src/chromiumos/tast/remote/bundles/cros/policy. With the generated service we can now implement the remote part of the test. For that we import all packages containing services we need as well as the rpc package. For tests involving enrollment we also need the remote/policyutil package to power wash the device.

import (
	ps "chromiumos/tast/services/cros/policy"

In the init() function we add the services we want to use as ServiceDeps. If the test performs an enrollment then we also add it to the enrollment group.

func init() {
		Func: SystemTimezone,
		Desc: "Just getting the time in a certain timezone",
		Contacts: []string{
			"googler@google.com", // Test author
		Attr:         []string{"group:enrollment"},
		SoftwareDeps: []string{"chrome"},
		ServiceDeps:  []string{"tast.cros.policy.PolicyService", "tast.cros.policy.SystemTimezoneService"},
		Timeout:      7 * time.Minute,

In the test function we then establish a gRPC connection to the DUT. We create a client instance of our service on the connection and then we can call the methods of the service.

func SystemTimezone(ctx context.Context, s *testing.State) {

	// Establish RPC connection to the DUT.
	cl, err := rpc.Dial(ctx, s.DUT(), s.RPCHint())
	if err != nil {
		s.Fatal("Failed to connect to the RPC service on the DUT: ", err)
	defer cl.Close(ctx)

	// Create client instance of the SystemTimezone service.
	psc := ps.NewSystemTimezoneServiceClient(cl.Conn)

	// Use the TestSystemTimezone method of the SystemTimezone service
	// to check if the timezone was set correctly by the policy.
	if _, err = psc.TestSystemTimezone(ctx, &ps.TestSystemTimezoneRequest{
		Timezone: "Europe/Berlin",
	}); err != nil {
		s.Error("Failed to set SystemTimezone policy : ", err)

The full implementation of the remote test can be found here.