In my very moderate experience (2^ kyu) the best test of your tecnique comes when training with the most beginner.
They neither oppose you with all their strenght (which can be pretty easy, if you know the tecnique in advance) nor help you ( which can be even worse then opposing, as it leaves you with the persuasion of a correct tecnique then it is not).
It's a real eye opener to try ikkio on some newcomer and realize it doesn't work because you forgot the correct breaking of balance at the beginning (all that high rank people expect you to do so, so they istinctively put themselves in the correct position).
One of the most pleasant experiences i ever had in aikido came a year or so ago while i was paired with someone on his first lessons. We were doing katate dori iriminage and it was his turn, so I backed up a little and prepared to grab his wrist. He suddently came with shomen uchi ( it was the attack for the previous tecnique he performed with someone else, we swich partner at every tecnique), and I performed shio nage without even thiking. He was on the ground before I realized what had happened.
This way I learned two thing:
1) I had been wondering if I could perform an appropriate tecnique without being prepared to it (randori, as it is practised slowly or declared at my level didn't provide a satsfying answer). Well, I can. Not only i didn't expect shomen uchi, i was not even expecting an attack!
2) I can perform shio nage on someone who doesn't know that tecnique and he won't spin off.