Diff viewer for tests no longer has the option to apply changes

In the past when developing my plugin I could easily update test-data files with the diff viewer when tests failed, as it used to show arrows I could click to apply the changed lines. This stopped working a while back probably due to some change in the testing framework. My question is how do I bring these back?

i have been doing manually copy and pasting between diff viewer and testdata files for smaller changes but now I am doing some larger refactoring and the annotations for many tests changes and doing the manual find the correct testdata file then copy & paste for 50-100 files is not something I am too keen on doing.