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.
PR #2088 is having major merge problems. This is partly because it moves some tests from Reader to Reader/Xlsx. Making this move beforehand may help. Or it may make things worse, but they are already bad enough that I am contemplating redoing the PR. If I do that, having this done beforehand will make things easier.
This PR does nothing but move some tests. This will make it easier to test changes to Xlsx Reader without having to run each test individually, or without having to run tests for all the other readers at the same time.