Change "mixed" declarations to more accurate types in test members; in particular, change those that would be flagged if we were to run Phpstan at level 9 (we currently run level 8). I may or may not follow up with source code (over 700 level-9 problems remain for src), but, as with strict typing, there is no reason to avoid the effort for test members.
It was necessary to update some doc blocks in src to accommodate this change. However, no executable code is touched.
While we might never be able to have 100% of our code strict, we can at
the very least do it for all of our tests. This ensures that our tests
are using our API with the types as intended by the test author, and not
silently be cast to what our API requires.
And quite a bit more manual changes. The idea is that typing of our
tests can be a bit more loose, so we assume PHPDoc is mostly correct. If
that happens to be wrong, it should be caught by the tests themselves.
Also enforce more rigorous Excel Function implementation by testing the underlying implementation, call via the Calc Engine, and execution from in a worksheet.
Separate out unhappy path (exception) checks into a separate test, so that a single test isn't made overcomplex checking for every potentiality.
Scrutinizer may dislike variadics, for variable number of arguments of mixed type; but tough. It's 100% valid PHP, accepted by phpstan, and makes life a lot easier.
Initial work here covers all the database and datetime unit tests for Excel function implementations.