# Flutter Tools

This section of the Flutter repository contains the command line developer tools
for building Flutter applications.

## Working on Flutter Tools

Be sure to follow the instructions on [CONTRIBUTING.md](../../CONTRIBUTING.md)
to set up your development environment. Further, familiarize yourself with the
[style guide](https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo),
which we follow.

### Setting up

First, ensure that the Dart SDK and other necessary artifacts are available by
invoking the Flutter Tools wrapper script. In this directory run:
```shell
$ flutter --version
```

### Running the Tool

To run Flutter Tools from source, in this directory run:
```shell
$ dart bin/flutter_tools.dart
```
followed by command-line arguments, as usual.


### Running the analyzer

To run the analyzer on Flutter Tools, in this directory run:
```shell
$ flutter analyze
```

### Writing tests

As with other parts of the Flutter repository, all changes in behavior [must be
tested](https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#write-test-find-bug).
Tests live under the `test/` subdirectory.
- Hermetic unit tests of tool internals go under `test/general.shard`.
- Tests of tool commands go under `test/commands.shard`. Hermetic tests go under
  its `hermetic/` subdirectory. Non-hermetic tests go under its `permeable`
  sub-directory. Avoid adding tests here and prefer writing either a unit test or a full
  integration test.
- Integration tests (e.g. tests that run the tool in a subprocess) go under
  `test/integration.shard`.

In general, the tests for the code in a file called `file.dart` should go in a
file called `file_test.dart` in the subdirectory that matches the behavior of
the test.

#### Using local engine builds in integration tests

The integration tests can be configured to use a specific local engine
variant by setting the `FLUTTER_LOCAL_ENGINE` environment variable to the
name of the local engine (e.g. "android_debug_unopt"). If the local engine build
requires a source path, this can be provided by setting the `FLUTTER_LOCAL_ENGINE_SRC_PATH`
environment variable. This second variable is not necessary if the `flutter` and
`engine` checkouts are in adjacent directories.

```shell
export FLUTTER_LOCAL_ENGINE=android_debug_unopt
flutter test test/integration.shard/some_test_case
```

### Running the tests

To run all of the unit tests:

```shell
$ flutter test test/general.shard
```

The tests in `test/integration.shard` are slower to run than the tests in
`test/general.shard`. Depending on your development computer, you might
want to increase timeouts and limit concurrency. Generally it is easier to run
these on CI, or to manually verify the behavior you are changing instead of running
the test.

The integration tests also require the `FLUTTER_ROOT` environment variable
to be set. The full invocation to run everything might therefore look something like:

```shell
$ FLUTTER_ROOT=~/path/to/flutter-sdk
$ flutter test --timeout 2x --concurrency 1
```

This will take about an hour to complete.

To run only the tests in `test/general.shard` (which takes about a minute),
in this directory run:
```shell
$ flutter test test/general.shard
```

To run the tests in a specific file, run:
```shell
$ flutter test test/general.shard/utils_test.dart
```

### Forcing snapshot regeneration

To force the Flutter Tools snapshot to be regenerated, delete the following
files:
```shell
$ rm ../../bin/cache/flutter_tools.stamp ../../bin/cache/flutter_tools.snapshot
```