The simplest solution would be to mark every page in your test environment "noindex". This is normally standard operating procedure anyway because most people don't want customers stumbling across the wrong URL in search by mistake and seeing a buggy page that isn't supposed to be "live" for customers.
Updating your robots.txt file would tell Google not to crawl the page, but if they've already crawled it and added it to their index it just means that they will retain the last crawled version of the page and will not crawl it in the future. You have to direct Google to "noindex" the pages. It will take some time as Google refreshes the crawl of each page, but eventually you'll see those errors drop off as Google removes those pages from their index. If I were consulting a client I would tell them to make the change and check back in two or three months.
Hope this helps!
