anchor.diff:          child: new StaggeredGridView(
               crossAxisSpacing: 0.0,
               mainAxisSpacing: 0.0,
  -            crossAxisCount: 4,
  +            crossAxisCount: crossAxisCount,
               staggeredTiles: tiles,
               children: widgets,
           ),
         )
       );
   
  -    const double cellLength = 200.0;
  +    List<Offset> expectedTopLeftNormalizedOffsets = const <Offset>[
  +      const Offset(0.0, 0.0),
  +      const Offset(2.0, 0.0),
  +      const Offset(3.0, 0.0),
  +      const Offset(2.0, 1.0),
   
  -    expect(tester.getTopLeft(find.text('0')), equals(const Offset(0.0, 0.0)));
  -    expect(tester.getTopLeft(find.text('1')), equals(const Offset(400.0, 0.0)));
  -    expect(tester.getTopLeft(find.text('2')), equals(const Offset(600.0, 0.0)));
  -    expect(tester.getTopLeft(find.text('3')), equals(const Offset(400.0, 200.0)));
  +      const Offset(0.0, 2.0),
   
  -    expect(tester.getTopLeft(find.text('4')), equals(const Offset(0.0, 400.0)));
  -    expect(tester.getTopLeft(find.text('5')), equals(const Offset(0.0, 600.0)));
  +      const Offset(0.0, 3.0),
   
  -    for (var i = 0; i < 6; ++i) {
  -      expect(tester.getSize(find.text('$i')), equals(_getTileSize(tiles[i],
  +      const Offset(0.0, 4.0),
  +      const Offset(1.0, 4.0),
  +      const Offset(2.0, 4.0),
  +      const Offset(3.0, 4.0),
  +
  +      const Offset(0.0, 5.0),
  +      const Offset(1.0, 5.0),
  +      const Offset(2.0, 5.0),
  +      const Offset(3.0, 5.0),
  +
  +      const Offset(3.0, 6.0),
  +      const Offset(2.0, 7.0),
  +      const Offset(3.0, 7.0),
  +      const Offset(1.0, 8.0),
  +      const Offset(2.0, 8.0),
  +      const Offset(3.0, 8.0),
  +    ];
  +
  +    for (var item in log) {
  +      expect(tester.getTopLeft(find.text('$item')), equals
  +        (expectedTopLeftNormalizedOffsets[item] * cellLength));
  +      expect(tester.getSize(find.text('$item')), equals(_getTileSize
  +        (tiles[item],
             cellLength)));
       }
   
  
positive.code: 
  void main() {
    testWidgets('StaggeredGridView - ', (WidgetTester tester) async {
      final List<int> log = <int>[];
      final widgets = new List<Widget>.generate(20, (int i){
        return new Builder(
  
negative.code: 
      final ScrollableState scrollableState = tester.state(find.byType(Scrollable));
      final ScrollPosition scrollPosition = scrollableState.position;
      scrollPosition.jumpTo(800.0);
  
      expect(log, isEmpty);
      await tester.pump();
  
      for (var item in log) {
        expect(tester.getTopLeft(find.text('$item')), equals
          (expectedTopLeftNormalizedOffsets[item] * cellLength  - const Offset
          (0.0, 800.0)));
        expect(tester.getSize(find.text('$item')), equals(_getTileSize
          (tiles[item],
            cellLength)));
      }
  
      expect(log, equals(<int>[
        6, 7, 8, 9,
  