There is randori in jodo. Perhaps not like the randori that you are used to in aikido or judo. Probably unlike any randori that you're familiar with, but it is a very interesting form of contest.
It is a contest of wills, and it takes place at the end of every kata. It is similar to the way that judo's katamenokata is an interesting mix of kata and randori - in katamenokata, tori applies a technique and uke makes three escape or counter attempts, then submits.
At the end of each jodo kata, the two participants face one another and the uke makes a signal that he is willing to stop fighting, but it is a small gesture - he is not submitting, he is conceding a minor point. Tori then makes a gesture, withdrawing the jo, testing the uke's sincerity. Then he makes another gesture towards peace, taking the jo offline, testing uke still. it is not until uke has committed to his second step backward that he has enough momentum towards a condition of peace, that tori begins withdrawing.
We often think of this osami as just a ceremonial ending to the kata, but you can also look at it as randori. It has the properties of randori...
- It is an engagement match with another participant
- Each participant is testing the other. Tori is watching for any provocation from uke that would continue the fight. Uke is watching for any flaw or weakness (suki) in tori's posture or position or kamae - anything that would allow uke to return to aggression with impunity. Uke is also watchig tori for any overt aggressive provocation - too much of which would be an indication of his insincerity.
- Either participant might "win" or "lose." The outcome is uncertain because it is not ever known which of the two will break first.
All of this takes the general form of a reverse arms race. Tension and suspicion is gradually allowed to subside, but there is always the possibility that the other participant is not what he seems, so both participants must keep kamae and exhibit zanshin.
This is a randori that takes place within the realm of the minds or the wills of the participants.