Tests/Exams or Demonstration of Skill
For the early ranks, especially, no one should be put up for their rank exams unless it is certain they will be able to execute the techniques for their rank passably well. This is the responsibility of the instructor. Some students may complete their hours of training and still not be ready.
I tell all my students that the hours for each rank are minimums not maximum.
The standards for each rank should be clearly posted and stated. While some students will always prepare only for the minimum, fortunately I have found them to be in the minority. The majority of students are anxious to show their instructor how well they are doing.
Generally, I view "tests" more as demonstrations of skill levels in a focused situation. After the student "passes" I then inform them they passed the first step for the rank. They must now earn their rank in the coming weeks and months. For this reason I do not present certificates or belts for the rank until well after the exam date to see if the student will continue training. I have heard from instructors over the years complaining that as soon as they handed out belts on test night, they did not see the students again.
In the advanced ranks, while there are still specific arts required, the advanced student should be able to handle "surprises" and mutliple ukes. At the same time, the advanced student should also be able to control their techniques much better so as to not injure their ukes.
Yudansha should be able to execute most any art well and show an increased intellectual understanding of the Aikido fundamentals as well.
Just some ramblings from an increasingly older Aikidoka.