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Here is the test I have locally, it draws the scrim with the color, that I validated visually, but how do I check it using a test?

testWidgets('ZoomPageTransition respects scrim color when set', (WidgetTester tester) async {
    final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
      '/': (BuildContext context) => Material(
        child: TextButton(
          child: const Text('push'),
          onPressed: () { Navigator.of(context).pushNamed('/b'); },
        ),
      ),
      '/b': (BuildContext context) => Container(color: const Color(0xff00ff00)),
    };

    await tester.pumpWidget(
      MaterialApp(
        routes: routes,
        theme: ThemeData(
          pageTransitionsTheme: const PageTransitionsTheme(
            builders: <TargetPlatform, PageTransitionsBuilder>{
              TargetPlatform.android: ZoomPageTransitionsBuilder(
                scrimColor: Color(0xffff0000),
              ),
            },
          ),
        ),
      ),
    );

    await tester.tap(find.text('push'));

    // Jump to the middle of the animation by pumping 8 frames, the scrim should be partially visible
    for (int i = 0; i < 8; i++) {
      await tester.pump(const Duration(milliseconds: 16));
    }

    final List<SnapshotWidget> snapshotWidgets = tester.widgetList(find.byType(SnapshotWidget)).cast<SnapshotWidget>().toList();

    // Filter only snapshots where the painter is ZoomEnterTransitionPainter going forward

    final List<ZoomEnterTransitionPainter> zoomTransitionPainters = snapshotWidgets.where((SnapshotWidget snapshot) {
      final SnapshotPainter painter = snapshot.painter;
      return painter is ZoomEnterTransitionPainter && !painter.reverse;
    }).map((SnapshotWidget snapshot) => snapshot.painter)
    .cast<ZoomEnterTransitionPainter>()
    .toList();

    final TestDisplay display = tester.binding.platformDispatcher.displays.first;
    final int width = display.size.width.toInt();
    final int height = display.size.height.toInt();
    for (final ZoomEnterTransitionPainter painter in zoomTransitionPainters) {
      final OffsetLayer offsetLayer = OffsetLayer();
      final PaintingContext context = PaintingContext(offsetLayer, Offset.zero & display.size);
      await tester.runAsync(() async {
        final ui.Image image = (await (await ui.ImageDescriptor.raw(
          await ui.ImmutableBuffer.fromUint8List(Uint8List.fromList(List<int>.filled(width * height * 4, 0xFF))),
          width: width,
          height: height,
          pixelFormat: ui.PixelFormat.rgba8888,
        ).instantiateCodec(targetHeight: height, targetWidth: width)).getNextFrame()).image;

        painter.paintSnapshot(context, Offset.zero, display.size, image, display.size, display.devicePixelRatio);
      });
    }
  }, variant: TargetPlatformVariant.only(TargetPlatform.android));

add tests to packages/flutter/test/material/page_transitions_theme_test.dart

@ElvisOkereke I know where to add them, the issue is that the class is private, I assume dynamic is not allowed in the official repo so how do I properly test it?

@QuncCccccc Sorry it took me so long, I changed the default parameter. But the question about the tests still holds.

Ping @QuncCccccc

@QuncCccccc Sorry it took me so long, I changed the default parameter. But the question about the tests still holds.

Maybe we can provide a golden test so we can visually see the color change for the scrim:) What do you think?

Yes that could be the "get out of jail free" card, however I have not created a golden test for this repository yet. I'll have to look at some existing examples on how the image files are handled.

There's another PR that seems to be fixing the same issue at #154057.

Yes that could be the "get out of jail free" card, however I have not created a golden test for this repository yet. I'll have to look at some existing examples on how the image files are handled.

Ah you can global search "matchesGoldenFile" for some examples:) We probably can wait that PR(#154057) lands first and then add this property. What do you think:)?

I think this PR should wait until the other one lands, then this PR can apply it's property to it, as well as use the test in the other PR as a basis to add another one.

Looks like #154057 is merged:)! @Michal-MK Can you help resolve the conflicts and add the property?

Hey, author of #154057 here! I wouldn't mind helping out with this if you want me to. It was tricky for me to figure how to test a change to an animation like this so I think I can help spare you the pain I went through, even if with that part only 👀

@dy0gu Hi thanks for the offer, I'll take a look at your test approach and attempt doing it myself (trying to learn, not to dismiss you <3). If I get stuck somewhere I will reach out. Today or over the weekend I'll get the PR ready.

@dy0gu In the end I just shamelessly copied your test, had no idea that paints is a global matcher that exists. Initially I was attempting to create the MockCanvas myself and somehow force the painter inside to use it. Your approach is infinitely simpler :D. I do understand what it does. And it avoids a golden which is nice.

@QuncCccccc I changed the code.