Pytest classes cannot have an __init__ method

[jeremyestein]

Several tests were being ignored in the system test.

[stefpiatek]

Ha yep that'd do it, frustrating that pytest fails silently here

[jeremyestein]

Ha yep that'd do it, frustrating that pytest fails silently here

One reason I'd like to do some mutation testing one day! If you change a load of your code and your tests still pass, your tests are probably broken.
A more down to earth measure might be to track test coverage over time so we can investigate any sudden drops.

[milanmlft]

A more down to earth measure might be to track test coverage over time so we can investigate any sudden drops.

Maybe worth adding to #331? -> #369

Also, sorry for this! This was part of fixing the mypy errors for #350, but did not realise the tests were failing 🙈