And how do you experience whether your technique is "good" or "works"? Can check your technique really only in randori?
You know your technique works if you've got an uke who's got the sincere intention to utterly destroy you with an attack and you can succesfully stay in control of the situation.
Since randori seems to be the ultimate goal in aikido, it should count as the best way to test whether or not your technique works. However, randori with bad ukes aren't all that either. Uke should always attack with the intent to hit or immobilize you.