Tast Quickstart (go/tast-quickstart)


You‘ll need a Chrome OS chroot. If you’ve only done Chrome development so far, note that this is different from the Chrome checkout described in the Simple Chrome documentation.

You‘ll also need a Chrome OS device running a system image built with the test flag that’s reachable from your workstation via SSH. An image running in a virtual machine will also work. If you‘re using a test image that you downloaded rather than one built in your chroot, make sure that it’s a recent version.

Run a prebuilt test

In your chroot, run the following:

tast -verbose run -build=false <test-device-ip> ui.ChromeLogin

You should see output scroll by on your workstation, and on the Chrome OS device, the test should log in and load a webpage. After the test is done, take a look at the results in /tmp/tast/results/latest in your chroot.

Build and run a test

The previous step ran a test that was already built into your device's system image, but you can also use the tast command to quickly rebuild all tests and push them to the device.

In your chroot, run the same command as before but without the -build=false argument:

tast -verbose run <test-device-ip> ui.ChromeLogin

This time, the command will take a bit longer (but build objects will be cached). The test should succeed again.

The first time you run this, or after you sync your checkout, you may see an error similar to the following:

The following dependencies are not installed:

To install them, please run the following in your chroot:
  cros_workon --host start 'chromeos-base/tast-local-tests-cros-9999'
  sudo emerge --jobs=16 --onlydeps --onlydeps-with-rdeps=n '=chromeos-base/tast-local-tests-cros-9999'

This is expected: to speed things up, tast is building the tests directly instead of emerging the tast-local-tests-cros package, so it needs some help from you to make sure that all required dependencies are installed. If you run the provided emerge command, the tast command should work when re-run.

See Running Tests for more information.

Modify a test

Now, let‘s modify the test. In your Chrome OS checkout, go to src/platform/tast-tests/src/chromiumos/tast/local/bundles/cros/ui and open chrome_login.go (for convenience, there’s also a local_tests symlink at the top of tast-tests). The ChromeLogin function here will run directly on the test device.

At the end of the function, add the following code:

if _, err = cr.NewConn(ctx, "https://www.google.com/"); err != nil {
	s.Error("Failed to open page: ", err)

Back in your chroot, run tast again:

tast -verbose run <test-device-ip> ui.ChromeLogin

This time, the test should additionally open a Google search page.

Return to the test file and add the following statement at the end of the function:

s.Error("This is an intentional error")

If you build and run the test again, you should see it fail.

See Writing Tests for more information, and explore the tast-tests repository to see existing tests and related packages.

Next steps

Additional Tast documentation is available in the tast repository.

Many resources are available for learning more about Go. Here are a few: