During golden test image comparison 2 lists of a different type are compared with the method "identical", so this will never be true. The test image is a _Uint8ArrayView while the master image is an Uint8List. So that results in always a heavy computation to get the difference between the test and the master image.

When you run this test snippet I go from 51 seconds to 14 seconds:
```dart
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  for (int i = 0; i < 100; i++) {
    testWidgets('Small test', (WidgetTester tester) async {
      await tester.pumpWidget(Directionality(textDirection: TextDirection.ltr, child: Text('jo')));
      await expectLater(find.byType(Text), matchesGoldenFile('main.png'));
    });
  }
}
```