How to automatically change the assignee from a group when transitioning the workflow using script

[Megha Mauni]

I need a script to change the assignee selected from a group for a transition in a round robin way.

for example: for every task if we are making a transition from todo to inprogress assignee should be selected from a group in a round robin way.

[Alex Christensen]

I don't know of any script that does this, but I know that Automation for Jira can do this. Here's a screenshot of a quick rule I configured that does this:

I haven't tried it in the free version of Automation for Jira, but it might be worth installing the free app into a development instance and seeing if that works for you.