Covering all these cases should actually be done in the unit tests of the CallbackValidator rather than through functional tests. It will be faster.

And I would add the check for ``array_of_functions["k"ey"]`` as invalid callback and ``array_of_functions["k\"ey"]`` as valid ones (as well as the single quote variants). I think the invalid cases are not catched by the current regex (and the provided valid cases are needed to ensure the fix is not too restrictive)