No rank past 3rd dan is actually tested for.
In the aikikai the grades up to yondan are tested, because they are considered to be technical grades. And studen-grades.
It all becomes political after that level.
Godan is the first teacher-grade in the traditional nomenclature.
So a godan is a teacher in his own rigtht and he will be redommended by his teacher and appointed by the aikikai.
I myself am a nidan, practicing since 15 years now. I only teach what I learn from my teacher (godan) and his teachers (7th and 8th dan).
My studends can verify my teaching when they train with my teacher or his teachers onseminars.
And from shodan on the gradings are tested by a jury of teachers from all over the country.
So I have to take the responsibility for what I teach.
My first teacher was nidan an had about 15 years of practice, when I asked him to be my teacher and he accepted me. I learned really a lot from him. He laid the foundation of the aikido, I#m dooing now.
It is an old tradition that the sempai teach the kohai. I learn a lot from teaching and it seems, that the students also learn from me.