public void GroupByHours() { var sw = Stopwatch.StartNew(); var result = _unitUnderTest9m.GroupByHours(3, a => a.First()).Rows; var result2 = _unitUnderTest9m.Group(c => c.ByTime.Hours(3).Aggregate(a => a.First())).Rows; result.SequenceEqual(result2).Should().BeTrue(); result.First().TimeUtc.Should().Be(new DateTime(2010, 1, 1, 12, 0, 0, DateTimeKind.Utc)); sw.Stop(); }