Setting up the test infrastructure, as suggested by Andras.
What would be useful is to have automated functional tests that would test features of the three tools. Interactive GUIs are hard to test comprehensively, so thorough automated testing of the Screenshot Annotation Editor may be hard, but both the Screenshot Capture and Screenshot Annotation Painter tools could be tested quite comprehensively without a lot of effort. Setting up the test infrastructure for this (GitHub action that can run the tests in a docker image in Slicer's Python environment)
Setting up the test infrastructure, as suggested by Andras.