New Post: Why does Should().ContainSingle() accept predicate mandatory

Comparing to LINQ having both Single() and Single(predicate), I want ContainSingle() overload accepting no parameters.
What analog does exist so far? HaveCount(1)?

Also even I specify predicate, I want ContainSingle().And. to return assertion against this single T but not initial IEnumerable<T>. Doesn't it make sense?