How to make transition from one state to another in workflow Follow

I am trying to create workflow

EG: If user has changed state from "Testing" back to "In progress"
He is forced to add comment.

Questions

1. How to write statement when state changes from one to another ? ( !State.becomes ({In progress]) && State.oldValue..... ? )
2. How to ensure that comments / spent time is always changed on every state change.
Now, if I write comments.required - System won't ask for another comment when one comment already exists. Same with spent time, if I require to enter spent time on every state change, it only asks for the first time.

Also, regarding comments.required  - command dialog opens - Sate In progress comments. What kind of function "comments" do as I have to delete it and write comment into comment section instead. I added attachment for this