refactor tests for invalid format items

[goatshriek]

Tests for names and other elements with formatting errors use much of the same code, and could be made more compact by refactoring the common code into helper test functions. Some documentation on creating and using test helpers can be found in test/README.md and docs/test.md

See the discussion of #184 for the context behind this request.

[Marecek460]

Hello. I would like to help work on this issue.

[goatshriek]

Absolutely! I have assigned the issue to you to mark it as in work. This issue is admittedly a little vague, so please reach out if you have any questions or need clarification.

[goatshriek]

Hello @Marecek460, just checking to see if you still intend to work on this? No worries if not, just want to see if this should be released for others.

[goatshriek]

This item is open for others to tackle once more.

[goatshriek]

Resolved by #474.