Rewrite doctest as unit test

[MetRonnie]

Closes #4413

This rewrite was handled by GitHub Copilot

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor. (But GitHub Copilot has not added themselves...)
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• No dependency changes
• Tests
• Not a change that can affect users
• Docs not required
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

Not the most suitable doctest, but I don't get the motive for translating it?

[MetRonnie]

To avoid the hacky patching of LOG.warning in the doctest. Why tackle this issue now? Simply to test out the capabilities of Copilot

[oliver-sanders]

Ah, hadn't spotted the attached issue, sorry, must read better.

[oliver-sanders]

Blocked by copilot approval?

[MetRonnie]

Blocked by copilot approval?

No, as mentioned on Teams the guidance wasn't clear that Copilot has been approved for this trial.

Anyway, if I was going to manually convert this test the code would have been 100% identical...

[hjoliver]

(Added blocked label pending approval at your end).

[MetRonnie]

Ok, Oliver wants to take this PR as an opportunity to have the generative AI guidance at our end improved as it's still a bit unworkable in its current draft

[MetRonnie]

Unblocked