This document describes how to make changes to the Tast framework itself. For information about writing Tast tests, see Writing Tests.
See the Overview document for a high-level description of the key components and terminology in Tast.
tastprocess over an SSH connection. It collects system information and initiates running local tests.
tastprocess to initiate running remote tests.
Shared library packages are located under the tast directory. Several packages are particularly important:
tastprocess, test runners, and test bundles.
JSON-marshaled structs are used for communication between processes:
The runner.Args and bundle.Args structs contain other
Args-suffixed structs that may or may not be set depending on the type of request that is being made. Note also that runner.RunTestsArgs includes bundle.RunTestsArgs and that runner.ListTestsArgs includes bundle.ListTestsArgs.
When running in the Chrome OS hardware lab or on VM builders, matching versions of
tast, test runners, and test bundles are used, so there are no compatibility concerns.
More combinations are possible when running in a developer's chroot:
tastbinary in the chroot can be updated by emerging
remote_test_runnerbinary in the chroot is typically updated by emerging
local_test_runnerbinary on the DUT can either be installed by the
tast-local-test-runnerpackage or updated by running
tast run -build=true.
tast-local-tests-crospackage or updated by running
tast run -build=true.
As a result, developers may end up running the
tast executable in their chroot against DUTs that contain either older or newer versions of
local_test_runner and test bundles. To maintain compatibility, please ensure that the following conditions hold across both the
tast-to-runner and runner-to-bundle boundaries:
Go‘s json package does best-effort unmarshaling, ignoring unknown fields by default. When renaming or moving a field, it’s advisable to preserve the old field for at least two months. Add a
Deprecated suffix to the old field's name while preserving its original marshaled name in its
tast and the runner package should set both the old and new fields, and the runner and bundle packages should copy the old fields to the new fields when the former are provided. See change 1474620 for an example.
The quickest way to rebuild the
tast executable after modifying its code is by running the fast_build.sh script located at the top of the
src/platform/tast repository within the Chrome OS chroot. This script bypasses Portage and runs
go build directly, allowing it to take advantage of Go's build cache. Since dependency checks are skipped, there's no guarantee that the resulting executable is correct – before uploading a change, you should verify it that it builds when you run
FEATURES=test sudo emerge tast-cmd (after running
cros_workon --host start tast-cmd).
fast_build.sh -t chromiumos/tast/testingruns the unit tests for the
fast_build.sh -Truns all unit tests (including ones in the
fast_build.sh -c chromiumos/tast/testingruns
go vetagainst the
fast_build.sh -Cvets all packages.
fast_build.sh -h to see all available options.
The different components of the framework are extensively covered by unit tests. Please ensure that any changes that you make are also covered by tests.
The testutil package provides utility functions intended to reduce repetitive code within unit tests.
There are several meta tests. These are remote Tast tests that run a nested instance of the
tast executable to perform end-to-end verification of interactions between
tast, test runners, and test bundles. They're executed the same way as other Tast tests, i.e. via