flutter/dev/devicelab/README.md

# Flutter DeviceLab

DeviceLab is a physical lab that tests Flutter on real devices.

This package contains the code for the test framework and tests. More generally
the tests are referred to as "tasks" in the API, but since we primarily use it
for testing, this document refers to them as "tests".

Current statuses for the devicelab are available at
<https://flutter-dashboard.appspot.com/#/build>. See [dashboard user
guide](https://github.com/flutter/cocoon/blob/main/dashboard/USER_GUIDE.md)
for information on using the dashboards.

## Table of Contents

* [How the DeviceLab runs tests](#how-the-devicelab-runs-tests)
* [Running tests locally](#running-tests-locally)
* [Writing tests](#writing-tests)
* [Adding tests to continuous
  integration](#adding-tests-to-continuous-integration)
* [Adding tests to presubmit](#adding-tests-to-presubmit)
* [Migrating to build and test model](#migrating-to-build-and-test-model)

## How the DeviceLab runs tests

DeviceLab tests are run against physical devices in Flutter's lab (the
"DeviceLab").

Tasks specify the type of device they are to run on (`linux_android`, `mac_ios`,
`mac_android`, `windows_android`, etc). When a device in the lab is free, it
will pickup tasks that need to be completed.

1. If the task succeeds, the test runner reports the success and uploads its
performance metrics to Flutter's infrastructure. Not all tasks record
performance metrics.
2. If task fails, an auto rerun happens. Whenever the last run succeeds, the
task will be reported as a success. For this case, a flake will be flagged and
populated to the test result.
3. If the task fails in all reruns, the test runner reports the failure to
   Flutter's infrastructure and no performance metrics are collected

## Running tests locally

Do make sure your tests pass locally before deploying to the CI environment.
Below is a handful of commands that run tests in a similar way to how the
CI environment runs them. These commands are also useful when you need to
reproduce a CI test failure locally.

### Prerequisites

You must set the `ANDROID_SDK_ROOT` environment variable to run
tests on Android. If you have a local build of the Flutter engine, then you have
a copy of the Android SDK at `.../engine/src/third_party/android_tools/sdk`.

You can find where your Android SDK is using `flutter doctor -v`.

### Warnings

Running the devicelab will do things to your environment.

Notably, it will start and stop Gradle, for instance.

### Running specific tests

To run a test, use option `-t` (`--task`):

```sh
# from the .../flutter/dev/devicelab directory
../../bin/cache/dart-sdk/bin/dart bin/test_runner.dart test -t {NAME_OF_TEST}
```

Where `NAME_OR_PATH_OF_TEST` is the name of a task, which is a file's
basename in `bin/tasks`. Example: `complex_layout__start_up`.

To run multiple tests, repeat option `-t` (`--task`) multiple times:

```sh
../../bin/cache/dart-sdk/bin/dart bin/run.dart -t test1 -t test2 -t test3
```

### Running tests against a local engine build

To run device lab tests against a local engine build, pass the appropriate
flags to `bin/run.dart`:

```sh
../../bin/cache/dart-sdk/bin/dart bin/run.dart --task=[some_task] \
  --local-engine-src-path=[path_to_local]/engine/src \
  --local-engine=[local_engine_architecture] \
  --local-engine-host=[local_engine_host_architecture]
```

An example of a local engine architecture is `android_debug_unopt_x86` and
an example of a local engine host architecture is `host_debug_unopt`.

### Running an A/B test for engine changes

You can run an A/B test that compares the performance of the default engine
against a local engine build. The test runs the same benchmark a specified
number of times against both engines, then outputs a tab-separated spreadsheet
with the results and stores them in a JSON file for future reference. The
results can be copied to a Google Spreadsheet for further inspection and the
JSON file can be reprocessed with the `summarize.dart` command for more detailed
output.

Example:

```sh
../../bin/cache/dart-sdk/bin/dart bin/run.dart --ab=10 \
  --local-engine=host_debug_unopt \
  --local-engine-host=host_debug_unopt \
  -t bin/tasks/web_benchmarks_canvaskit.dart
```

The `--ab=10` tells the runner to run an A/B test 10 times.

`--local-engine=host_debug_unopt` tells the A/B test to use the
`host_debug_unopt` engine build. `--local-engine-host=host_debug_unopt` uses
the same engine build to run the `frontend_server` (in this example).
`--local-engine` is required for A/B test.

`--ab-result-file=filename` can be used to provide an alternate location to
output the JSON results file (defaults to `ABresults#.json`). A single `#`
character can be used to indicate where to insert a serial number if a file with
that name already exists, otherwise, the file will be overwritten.

A/B can run exactly one task. Multiple tasks are not supported.

Example output:

```text
Score	Average A (noise)	Average B (noise)	Speed-up
bench_card_infinite_scroll.canvaskit.drawFrameDuration.average	2900.20 (8.44%)	2426.70 (8.94%)	1.20x
bench_card_infinite_scroll.canvaskit.totalUiFrame.average	4964.00 (6.29%)	4098.00 (8.03%)	1.21x
draw_rect.canvaskit.windowRenderDuration.average	1959.45 (16.56%)	2286.65 (0.61%)	0.86x
draw_rect.canvaskit.sceneBuildDuration.average	1969.45 (16.37%)	2294.90 (0.58%)	0.86x
draw_rect.canvaskit.drawFrameDuration.average	5335.20 (17.59%)	6437.60 (0.59%)	0.83x
draw_rect.canvaskit.totalUiFrame.average	6832.00 (13.16%)	7932.00 (0.34%)	0.86x
```

The output contains averages and noises for each score. More importantly, it
contains the speed-up value, i.e. how much _faster_ is the local engine than
the default engine. Values less than 1.0 indicate a slow-down. For example,
0.5x means the local engine is twice as slow as the default engine, and 2.0x
means it's twice as fast. Higher is better.

Summarize tool example:

```sh
../../bin/cache/dart-sdk/bin/dart bin/summarize.dart  --[no-]tsv-table --[no-]raw-summary \
    ABresults.json ABresults1.json ABresults2.json ...
```

`--[no-]tsv-table` tells the tool to print the summary in a table with tabs for
easy spreadsheet entry. (defaults to on)

`--[no-]raw-summary` tells the tool to print all per-run data collected by the
A/B test formatted with tabs for easy spreadsheet entry. (defaults to on)

Multiple trailing filenames can be specified and each such results file will be
processed in turn.

## Reproducing broken builds locally

To reproduce the breakage locally `git checkout` the corresponding Flutter
revision. Note the name of the test that failed. In the example above the
failing test is `flutter_gallery__transition_perf`. This name can be passed to
the `run.dart` command. For example:

```sh
../../bin/cache/dart-sdk/bin/dart bin/run.dart -t flutter_gallery__transition_perf
```

## Writing tests

A test is a simple Dart program that lives under `bin/tasks` and uses
`package:flutter_devicelab/framework/framework.dart` to define and run a _task_.

Example:

```dart
import 'dart:async';

import 'package:flutter_devicelab/framework/framework.dart';

Future<void> main() async {
  await task(() async {
    ... do something interesting ...

    // Aggregate results into a JSONable Map structure.
    Map<String, dynamic> testResults = ...;

    // Report success.
    return new TaskResult.success(testResults);

    // Or you can also report a failure.
    return new TaskResult.failure('Something went wrong!');
  });
}
```

Only one `task` is permitted per program. However, that task can run any number
of tests internally. A task has a name. It succeeds and fails independently of
other tasks, and is reported to the dashboard independently of other tasks.

A task runs in its own standalone Dart VM and reports results via Dart VM
service protocol. This ensures that tasks do not interfere with each other and
lets the CI system time out and clean up tasks that get stuck.

## Adding tests to continuous integration

Host only tests should be added to `flutter_tools`.

There are several PRs needed to add a DeviceLab task to CI.

_TASK_- the name of your test that also matches the name of the
  file in `bin/tasks` without the `.dart` extension.

1. Add target to
   [.ci.yaml](https://github.com/flutter/flutter/blob/main/.ci.yaml)
   * Mirror an existing one that has the recipe `devicelab_drone`

If your test needs to run on multiple operating systems, create a separate
target for each operating system.

## Adding tests to presubmit

Flutter's DeviceLab has a limited capacity in presubmit. File an infra ticket
to investigate feasibility of adding a test to presubmit.

## Migrating to build and test model

To better utilize limited DeviceLab testbed resources and speed up commit validation
time, it is now supported to separate building artifacts (.apk/.app) from testing them.
The artifact will be built on a host only bot, a VM or physical bot without a device,
and the test will run based on the artifact against a testbed with a device.

Steps:

1. Update the task class to extend [`BuildTestTask`](https://github.com/flutter/flutter/blob/main/dev/devicelab/lib/tasks/build_test_task.dart)
   - Override function `getBuildArgs`
   - Override function `getTestArgs`
   - Override function `parseTaskResult`
   - Override function `getApplicationBinaryPath`
2. Update the `bin/tasks/{TEST}.dart` to point to the new task class
3. Validate the task locally
   - build only: `dart bin/test_runner.dart test -t {NAME_OR_PATH_OF_TEST} --task-args build --task-args application-binary-path={PATH_TO_ARTIFACT}`
   - test only: `dart bin/test_runner.dart test -t {NAME_OR_PATH_OF_TEST} --task-args test --task-args application-binary-path={PATH_TO_ARTIFACT}`
4. Add tasks to continuous integration
   - Mirror a target with platform `Linux_build_test` or `Mac_build_test`
   - The only difference from regular targets is the artifact property: if omitted, it will use the `task_name`.
5. Once validated in CI, enable the target in `PROD` by removing `bringup: true` and deleting the old target entry without build+test model.

Take gallery tasks for example:

1. Linux android
   - Separating PR: https://github.com/flutter/flutter/pull/103550
   - Switching PR: https://github.com/flutter/flutter/pull/110533
2. Mac iOS: https://github.com/flutter/flutter/pull/111164