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.
Fix for #2082. Xlsx Writer was writing a cell which is a formula which evaluates to boolean false as an empty XML tag. This is okay for Excel 365, but not for Excel 2016-. Change to write the tag as a value of 0 instead, which works for all Excel releases. Add test.
Adrien Crivelli
Owen Leibman