flutter/dev/devicelab/README.md

# Flutter devicelab

"Devicelab" (a.k.a. [Cocoon](https://github.com/flutter/cocoon)) is a physical
lab that tests Flutter on real Android and iOS devices.

This package contains the code for test framework and the 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.

# Dashboards

## Build dashboard

The build page is accessible at https://flutter-dashboard.appspot.com/#/build.
This page reports the build statuses of commits to the flutter/flutter repo.

### Tasks

Task statuses are color-coded in the following manner:

**New task** (blue): the task is waiting for an agent to pick it up and
start the build.

**Task is running** (blue with clock): an agent is currently building the task.

**Task succeeded** (green): an agent reported a successful completion of the
task.

**Task is flaky** (yellow): the task was attempted multiple time, but only the
latest attempt succeeded (we currently only try twice).

**Task failed** (red): the task failed all of the attempts.

**Task is rerunning** (orange): the task is being rerun.

**Task was skipped** (transparent): the task is not scheduled for a build. This
usually happens when a task is removed from `manifest.yaml` file.

In addition to color-coding, a task may display a question mark. This means
that the task was marked as flaky manually. The status of such task is ignored
when considering whether the build is broken or not. For example, if a flaky
task fails, GitHub will not prevent PR submissions. However, if the latest
status of a non-flaky task is red, all pending PRs will contain a warning about
the broken build and recommend caution when submitting.

Clicking a cell will pop up an overlay with information about that task. It
includes information such as the task name, number of attempts, run time,
queue time, whether it is manually marked flaky, and the agent it was run on.
It has actions to download the log, rerun the task, and view the agent on
the agent dashboard.

## Why is a task stuck on "new task" status?

The dashboard aggregates build results from multiple build environments,
including Cirrus, Chrome Infra, and devicelab. While devicelab
tests every commit that goes into the `master` branch, other environments
may skip some commits. For example, Cirrus will only test the
_last_ commit of a PR that's merged into the `master` branch. Chrome Infra may
skip commits when they come in too fast.

## Agent dashboard

Agent statuses are available at https://flutter-dashboard.appspot.com/#/agents.

A green agent is considered healthy and ready to receive new tasks to build. A
red agent is broken and does not receive new tasks.

## Performance dashboard

Flutter benchmarks are available at
https://flutter-dashboard.appspot.com/benchmarks.html.

# How the devicelab runs tasks

The devicelab agents have a small script installed on them that continuously
asks the CI server for tasks to run. When the server finds a suitable task for
an agent it reserves that task for the agent. If the task succeeds, the agent
reports the success to the server and the dashboard shows that task in green.
If the task fails, the agent reports the failure to the server, the server
increments the counter counting the number of attempts it took to run the task
and puts the task back in the pool of available tasks. If a task does not
succeed after a certain number of attempts (as of this writing the limit is 2),
the task is marked as failed and is displayed using red color on the dashboard.

# 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 `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`.

## Warnings

Running devicelab will do things to your environment.

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

## Running all tests

To run all tests defined in `manifest.yaml`, use option `-a` (`--all`):

```sh
../../bin/cache/dart-sdk/bin/dart bin/run.dart -a
```

This defaults to only running tests supported by your host device's platform
(`--match-host-platform`) and exiting after the first failure (`--exit`).

## 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/run.dart -t {NAME_OR_PATH_OF_TEST}
```

Where `NAME_OR_PATH_OF_TEST` can be either of:

- the _name_ of a task, which you can find in the `manifest.yaml` file in this
  directory. Example: `complex_layout__start_up`.
- the path to a Dart _file_ corresponding to a task, which resides in `bin/tasks`.
  Tip: most shells support path auto-completion using the Tab key. Example:
  `bin/tasks/complex_layout__start_up.dart`.

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
```

To run tests from a specific stage, use option `-s` (`--stage`).
Currently there are only three stages defined, `devicelab`,
`devicelab_ios` and `devicelab_win`.


```sh
../../bin/cache/dart-sdk/bin/dart bin/run.dart -s {NAME_OF_STAGE}
```

## 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]
```

An example of a local engine architecture is `android_debug_unopt_x86`.

## 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 \
  -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` 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:

```
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 the CI environment

The `manifest.yaml` file describes a subset of tests we run in the CI. To add
your test edit `manifest.yaml` and add the following in the "tasks" dictionary:

```
  {NAME_OF_TEST}:
    description: {DESCRIPTION}
    stage: {STAGE}
    required_agent_capabilities: {CAPABILITIES}
```

Where:

 - `{NAME_OF_TEST}` is the name of your test that also matches the name of the
 file in `bin/tasks` without the `.dart` extension.
 - `{DESCRIPTION}` is the plain English description of your test that helps
 others understand what this test is testing.
 - `{STAGE}` is `devicelab` if you want to run on Android, or `devicelab_ios` if
 you want to run on iOS.
 - `{CAPABILITIES}` is an array that lists the capabilities required of
 the test agent (the computer that runs the test) to run your test. As of writing,
 the available  capabilities are: `linux`, `linux/android`, `linux-vm`,
`mac`, `mac/ios`, `mac/iphonexs`, `mac/ios32`, `mac-catalina/ios`,
`mac-catalina/android`, `ios/gl-render-image`, `windows`, `windows/android`.

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