public void TestPaging()
        {
            var data = new[]
            {
                Point(now), Point(now.PlusDays(5)), Point(now.PlusDays(20)),
                Point(now.PlusDays(21)), Point(now.PlusDays(25)),
                Point(now.PlusDays(50))
            };

            var expected = new[]
            {
                new[] { Point(now), Point(now.PlusDays(5)), Point(now.PlusDays(20)) },
                new[] { Point(now.PlusDays(21)), Point(now.PlusDays(25)) },
                new[] { Point(now.PlusDays(50)) }
            };

            var actual = ChartWriter.Group(data).Select(list => list.ToArray()).ToArray();

            AssertArraysEqual(expected, actual);
        }