public void A_FlattenMerge_must_not_be_held_back_by_one_slow_stream()
{
var task = Source.From(new[] { Src10(0), Src10(10), Blocked, Src10(20), Src10(30) })
.MergeMany(3, s => s)
.Take(40)
.RunWith(ToSet, Materializer);
task.Wait(TimeSpan.FromSeconds(1)).Should().BeTrue();
task.Result.ShouldAllBeEquivalentTo(Enumerable.Range(0, 40));
}