public void GroupBy_must_work_in_normal_user_scenario()
{
var source = Source.From(new[] {"Aaa", "Abb", "Bcc", "Cdd", "Cee"})
.GroupBy(3, s => s.Substring(0, 1))
.Grouped(10)
.MergeSubstreams()
.Grouped(10);
var task =
((Source<IEnumerable<IEnumerable<string>>, NotUsed>) source).RunWith(
Sink.First<IEnumerable<IEnumerable<string>>>(), Materializer);
task.Wait(TimeSpan.FromSeconds(3)).Should().BeTrue();
task.Result.OrderBy(e => e.First())
.ShouldBeEquivalentTo(new[] {new[] {"Aaa", "Abb"}, new[] {"Bcc"}, new[] {"Cdd", "Cee"}});
}