I really appreciate working with testers but the usual workflow for testing is something like
[i make pull request] -> [manager makes change to test system] -> [tester tests it]
This cycle takes a while, at the very least an hour but sometimes a few days. I find I spend a good chunk of time testing things thoroughly before I send it through this workflow because I don't want to waste the time of the team and start a cycle because of a "stupid" error on my part. I feel though that if I worker closer to the tester I wouldn't be testing things myself so much and could spend more time designing, coding, etc.
I also find that I spend a significant amount of time setting up test data on my dev system. Sometimes it is maybe 10% of the effort on a task but it is sometimes 90%.
Has anyone worked in a situation where you have very close integration with a tester, that is, the tester is at a desk next to you and the cycle to throw something over to them is a few minutes instead of a few hours?