An easy non-aggressive way to test yours and others level of ability, understanding, and knowledge of Aikido.
Just grab someone's wrist tight and have them perform Irimi Tenkan. If they are able to do this quite easily with no force, without trying to hit or distract you, then they have a good level of knowledge and understanding. If it is difficult, then more work is obviously required.
You can use this small simple test throughout your Aikido journey to gauge yours and others level of improvement (or lack of).
This is also a very good way to assist in finding a good teacher as well, just ask if it is OK first. Any decent teacher will just smile and offer both wrists to you, so you can choose which one to grab.
I strongly believe that the "Secrets of Aikido" are in the basics.
Do not make the mistake of rushing past the basics to try and obtain all those flashy techniques.
If your basics are weak, then so shall your Aikido be.
Enjoy the journey.
I am very interested in how this comment of mine has produced many various and interesting thoughts and opinions. Keep it up, and well done.