Another thought related to characterisation testing, this time from Jeremias Roessler's talk at QAFest Ukraine 2017 (https://www.youtube.com/watch?v=f4PT_u8hjhU): Traditional automated tests (with asserts) are "blacklisting" the changes that aren't allowed, whereas a characterisation test will catch any change in behaviour, and instead you have to "whitelist" the changes that are allowed (by providing regexes or some kind of pattern to match the dynamic output that is allowed to change).