anchor.diff:  
       // Drag the scrollable up and down. The app bar should not snap open, its
       // height should just track the the drag offset.
  -    TestGesture gesture = await tester.startGesture(const Point(50.0, 256.0));
  +    TestGesture gesture = await tester.startGesture(const Offset(50.0, 256.0));
       await gesture.moveBy(const Offset(0.0, 128.0)); // drag the appbar all the way open
       await tester.pump();
       expect(appBarTop(tester), 0.0);
  
positive.code: 
      // Drag the scrollable up and down. The app bar should not snap open, the
      // bottof of the appbar should just track the drag offset.
      TestGesture gesture = await tester.startGesture(const Point(50.0, 200.0));
      await gesture.moveBy(const Offset(0.0, 100.0));
      await tester.pump();
      expect(appBarHeight(tester), 100.0);
  
negative.code:     // Now that the appbar is fully expanded, Perform the same drag
      // scenario in reverse: drag the appbar up and down and then trigger
      // the snap closed animation.
      gesture = await tester.startGesture(const Offset(50.0, 256.0));
      await gesture.moveBy(const Offset(0.0, -128.0));
      await tester.pump();
      expect(appBarBottom(tester), kTextTabBarHeight);
  