# Integration test default golden-file comparators changed on Android and iOS.

> When using `package:integration_test` to run a test _on_ an Android device or emulator, or an iOS device or simulator, the default `goldenFileComparator` has changed, and correctly uses the host filesystem.




:::important
These breaking change docs are accurate, as of the release
under which they are published. Over time, the
workarounds described here might become inaccurate.
We don't, in general, keep these breaking change docs up
to date as of each release.

The [breaking change index file](/release/breaking-changes)
lists the docs created for each release.
:::


## Summary

Unless a user-defined [`goldenFileComparator`][] is set, either manually in a
test, or using a `flutter_test_config.dart` file, Android and iOS devices
and emulators/simulators have a new default that proxies to the local host
filesystem, fixing a long-standing bug ([#143299][Issue 143299]).

## Background

The package [`integration_test`][], and its integration with [`flutter_test`][]
has historically had a bug where using [`matchesGoldenFile`][] or similar APIs
where a `FileSystemException` was thrown.

Some users may have worked around this issue by writing and using a custom
[`goldenFileComparator`][]:

```dart
import 'package:integration_test/integration_test.dart';
import 'package:my_integration_test/custom_golden_file_comparator.dart';

void main() {
  goldenFileComparator = CustomGoldenFileComparatorThatWorks();

  // ...
}
```

Such workarounds are no longer necessary, and if type checking the default,
will no longer work as before:

```dart
if (goldenFileComparator is ...) {
  // The new default is a new (hidden) type that has not existed before.
}
```

## Migration guide

In most cases, we expect users to have to do nothing - this will be in a sense
_new_ functionality that replaced functionality that did not work and caused
an unhandled exception which would fail a test.

In cases where users wrote custom test infrastructure and comparators, consider
instead removing the [`goldenFileComparator`][] overrides, and instead rely on
the (new) default which should work as expected:

```dart diff
  import 'package:integration_test/integration_test.dart';
- import 'package:my_integration_test/custom_golden_file_comparator.dart';

  void main() {
-   goldenFileComparator = CustomGoldenFileComparatorThatWorks();

    // ...
  }
```

_Fun fact_: The existing code that was used for
the _web_ platform was [reused][PR 160484].

## Timeline

Landed in version: 3.29.0-0.0.pre<br>
Stable release: 3.32

## References

Relevant APIs:

- [`flutter_test`][], which talks about `flutter_test_config.dart` and its capabilities.
- [`goldenFileComparator`][], which implements comparison, and is user-configurable.

Relevant Issues:

- [Issue 143299][], one of many user reports about the long-standing bug.
- [Issue 160043][], which explains in technical detail why [`matchesGoldenFile`][] failed.

Relevant PRs:

- [PR 160215][], where the web tool implementation was refactored to make it generic.
- [PR 160484][], which uses the Dart VM service protocol to proxy between device and host.

[`flutter_test`]: https://api.flutter.dev/flutter/flutter_test
[`goldenFileComparator`]: https://api.flutter.dev/flutter/flutter_test/goldenFileComparator.html
[`integration_test`]: https://api.flutter.dev/flutter/package-integration_test_integration_test/
[Issue 143299]: https://github.com/flutter/flutter/issues/143299
[Issue 160043]: https://github.com/flutter/flutter/issues/160043
[`matchesGoldenFile`]: https://api.flutter.dev/flutter/flutter_test/MatchesGoldenFile-class.html
[PR 160215]: https://github.com/flutter/flutter/pull/160215
[PR 160484]: https://github.com/flutter/flutter/pull/160484