Add a test for checking the format of the LLM output

[dearden]

Fixes #93.

Adds another test which checks if the generated output is in the correct format.

---

Pull request checklist

• [ ] I have linked my PR to an issue
• [ ] I’ve used conventional commits
• [ ] My branch is up-to-date with main
• [ ] Where appropriate, I have added or updated tests
• [ ] Where appropriate, I have updated documentation to reflect my changes