test: cover serialization and deserialization of formulas

The serialization and deserialization of Formulas is not tested by the current examples. Thus lines 481-495 of the json_deserilization, lines 169-173 of the json_serialization and lines 213-219 of the xml_serialization are not covered.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information