Is there some formal way(s) of quantifying potential flaws, or risk, and ensuring there’s sufficient spread of tests to cover them? Perhaps using some kind of complexity measure? Or a risk assessment of some kind?
Experience tells me I need to be extra careful around certain things - user input, code generation, anything with a publicly exposed surface, third-party libraries/services, financial data, personal information (especially of minors), batch data manipulation/migration, and so on.
But is there any accepted means of formally measuring a system and ensuring that some level of test quality exists?
On top or, better, in addition to mutation testing, some amount of property-based testing is always great where it counts.
Additionally I like roundtrip tests.
For example we have two data formats and support conversion between both of them.
So I have tests that convert from A to B and back to A. Then I can go and call assertEquals on them.
It’s a very cheap test, that tests all functionality of the conversion itself.