For a database-driven application with sqlalchemy, I've found mixer[0] to be pretty helpful. It gives you an easy way to generate an object, and it automatically creates dummy-objects that your object depends on.
You can also supply defaults and name schemes for individual columns.
For business logic, I prefer to have it structured in a way that it doesn't need the database for testing, but loading and searching stuff from the DB also needs to be tested, and for those, mixer strikes a really good balance. You only need to specify the attributes that are relevant for the test, and you don't need shared fixtures between many tests.
The invoicing standard is an attempt to mitigate reverse charge fraud by gathering more machine-readable data. Some countries even demand that b2b invoices are sent to the country, which then dispatches a copy to the recipient.
Knowing this background, it's pretty clear why the EU is making it mandatory.
Personally, in the abstract I like the idea to mandate the use of an open standard, I think we have way too many inefficiencies from treating many things as text documents that could be data structures. I don't like this particular standard though, it's bloated and the result of a typical top-down process.
I much prefer it when there are competing standards for a while, and one or a couple of winner emerge on technical merits. THEN I have no objections to a regulatory body picking a standard and mandating it.