LocalFileComparator class

The default GoldenFileComparator implementation for flutter test.

The term golden file refers to a master image that is considered the true rendering of a given widget, state, application, or other visual representation you have chosen to capture. This comparator loads golden files from the local file system, treating the golden key as a relative path from the test file's directory.

This comparator performs a pixel-for-pixel comparison of the decoded PNGs, returning true only if there's an exact match. In cases where the captured test image does not match the golden file, this comparator will provide output to illustrate the difference, described in further detail below.

When using flutter test --update-goldens, LocalFileComparator updates the golden files on disk to match the rendering.

Local Output from Golden File Testing

The LocalFileComparator will output test feedback when a golden file test fails. This output takes the form of differential images contained within a failures directory that will be generated in the same location specified by the golden key. The differential images include the master and test images that were compared, as well as an isolated diff of detected pixels, and a masked diff that overlays these detected pixels over the master image.

The following images are examples of a test failure output:

File Name Image Output
testName_masterImage.png A golden master image
testName_testImage.png Test image
testName_isolatedDiff.png An isolated pixel difference.
testName_maskedDiff.png A masked pixel difference

Including Fonts

Custom fonts may render differently across different platforms, or between different versions of Flutter. For example, a golden file generated on Windows with fonts will likely differ from the one produced by another operating system. Even on the same platform, if the generated golden is tested with a different Flutter version, the test may fail and require an updated image.

By default, the Flutter framework uses a font called 'Ahem' which shows squares instead of characters, however, it is possible to render images using custom fonts. For example, this is how to load the 'Roboto' font for a golden test:

How to load a custom font for golden images.
testWidgets('Creating a golden image with a custom font', (WidgetTester tester) async {
  // Assuming the 'Roboto.ttf' file is declared in the pubspec.yaml file
  final Future<ByteData> font = rootBundle.load('path/to/font-file/Roboto.ttf');

  final FontLoader fontLoader = FontLoader('Roboto')..addFont(font);
  await fontLoader.load();

  await tester.pumpWidget(const MyWidget());

  await expectLater(

The example above loads the desired font only for that specific test. To load a font for all golden file tests, the FontLoader.load() call could be moved in the flutter_test_config.dart. In this way, the font will always be loaded before a test:

Loading a custom font from the flutter_test_config.dart file.
Future<void> testExecutable(FutureOr<void> Function() testMain) async {
  setUpAll(() async {
    final FontLoader fontLoader = FontLoader('SomeFont')..addFont(someFont);
    await fontLoader.load();

  await testMain();

See also:

Mixed in types


LocalFileComparator(Uri testFile, {Style? pathStyle})
Creates a new LocalFileComparator for the specified testFile.


basedir Uri
The directory in which the test was loaded.
hashCode int
The hash code for this object.
no setterinherited
runtimeType Type
A representation of the runtime type of the object.
no setterinherited


compare(Uint8List imageBytes, Uri golden) Future<bool>
Compares the pixels of decoded png imageBytes against the golden file identified by golden.
generateFailureOutput(ComparisonResult result, Uri golden, Uri basedir, {String key = ''}) Future<String>
Writes out diffs from the ComparisonResult of a golden file test.
getFailureFile(String failure, Uri golden, Uri basedir) File
Returns the appropriate file for a given diff from a ComparisonResult.
getGoldenBytes(Uri golden) Future<List<int>>
Returns the bytes of the given golden file.
getTestUri(Uri key, int? version) Uri
Returns a new golden file Uri to incorporate any version number with the key.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
toString() String
A string representation of this object.
update(Uri golden, Uint8List imageBytes) Future<void>
Updates the golden file identified by golden with imageBytes.


operator ==(Object other) bool
The equality operator.