We often change between "dancing" and "resistant" uke. Dancing is needed to keep nage soft or make him softer and more perceptive. The purpose of the "resistant training" is less to check if it works, but to check, if nage is still soft and perceptive - and thus the technique works. It works also the hard way, but that is not the intension of our training. Well there are also some exercises to ensure that we can change to the hard way, in case we need.
But first I like to rename some expressions. Uke should never be punished, but taught.
Example 1: "You'd better try not to keep your arm straight. It might spell this technique, but I can break your elbow easily" without any word - just show, what you could do.
Example 2 (better solution): "If you do this, I might not be able to do the shihonage, which I was told to, but I can easily change to kotegaeshi" again without any spoken word.
Example 3 (even better): "You try to stop my move? Oh it is easy to follow your intention a little bit, redirect it, change my position or angle to you just a little bit and do exactly, what I wanted to do".
Well it is a lie, it is absolutely not easy, but if a good aikidoka does it to you it looks so easy and natural, that you cannot believe, it was difficult - until you try.
And Uke should not really be resistant or non-resistant, he should be protective. That means his intent should not be to spoil your technique - which is easy to most nage, when you know, what he is told to do, and hist intent should not be to just do a stupid technique and unbalance himself on purpose. He should do a required technique in a way, that he is protected as good as possible against any counter-attack, which could include the technique to be trained, but should not based specifically on knowing, which technique should come.
The level of course depends on the skills of nage and uke and the purpose of the lesson.
Protective means also to escape greater harm. So if uke does not see a chance to continue the attack, he is allowed to roll out. He does not need to wait for pain, when it necessarily would come.
I have seen exaggeration on the last point.
"I know nikyo hurts, so I go down, before you take my wrist"
"I know you could kill me so I roll out before the attack started", which is a good idea in real life, but how can we do practice, then?
"If the technique would be done properly, I had to roll, so I roll, even though your technique would never work at all"
The the first two excuses are far away so that nobody would accept this, but I have seen them. The last one is close to border, depending how you read it. On my level, we still do it in a way "I feel, that the technique is at its end, so I roll for you. I guess, I had other choices, but at least I felt the direction and according to your level, there is nothing I need to correct now. Either it is sensei's task or I 'll do that later, probably in a few weeks."
My uke even do that for me, especially in kokyunage, but you could use this phrase probably for all my techniques
This is my humble opinion - not really humble, as I think of myself as a great aikidoka - at least in theory. But I am always humble enough to accept corrections on the mat and in the web. Even if they sometimes hurt and feel like punishment.
All the best