             assertEquals(errorMessageHeaderIndex, expectedHeaderIndex, actualHeaderIndex);
         }
 
+        private function assertThatColumnIndexIsCorrect(point:Point, pointName:String, currentTransformation:Matrix):void
+        {
+            //when
+            var expectedColumnIndex:int = getColumnIndexAssumption(point);
+            var actualColumnIndex:int = getColumnIndexAtGlobalPoint(point);
+            const errorMessageColumnIndex:String = getColumnIndexErrorMessage(pointName, currentTransformation, point, expectedColumnIndex, actualColumnIndex);
+
+            //then
+            assertEquals(errorMessageColumnIndex, expectedColumnIndex, actualColumnIndex);
+        }
+
         private function getHeaderIndexErrorMessage(pointName:String, direction:Matrix, transformedPoint:Point, expectedColumnHeaderIndex:int, actualColumnHeaderIndex:int):String
         {
             return "The point " + pointName + " transformed with Matrix " + direction + " (resulting in " + transformedPoint + ") should be "

            return _sut.getHeaderIndexAt(localPoint.x, localPoint.y);
        }

        private function getHeaderShouldContainPointAssumption(point:Point):Boolean
        {
            return rectangleContainsPoint(entireHeaderRectangle, point);

        private var _keyPoints:Array;

        //@TODO add cases with horizontal scroll, and also with fixed columns
        public static var dimensions:Array = [
            /*x, y, width, header padding left, header padding top, header padding bottom, [column widths] */
            [[/*x=*/    0, /*y=*/   0, /*width=*/   300, /*paddingLeft=*/   5, /*paddingTop=*/  0, /*paddingBottom=*/   0, /*columnWidths=*/[25, 150]]],
            [[/*x=*/   10, /*y=*/   0, /*width=*/   300, /*paddingLeft=*/   5, /*paddingTop=*/  0, /*paddingBottom=*/   5, /*columnWidths=*/[25, 150]]],
            [[/*x=*/   -5, /*y=*/-100, /*width=*/   200, /*paddingLeft=*/  25, /*paddingTop=*/ 12, /*paddingBottom=*/   5, /*columnWidths=*/[100, 150]]] //horizontal scroll
        ];


