Increase test coverage for --sniffs and --exclude options

[fredden]

Description

While working on #344, it was noted that there are no existing tests for the code being changed. This pull request aims to add some tests to cover the existing behaviour.

Suggested changelog entry

• Improve test coverage of internal functionality

Related issues/external references

Related to #344

Types of changes

• Chore - no functional changes, only code coverage

PR checklist

• I have checked there is no other PR open for the same change.
• I have read the Contribution Guidelines.
• I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• I have added tests to cover my changes.
• I have verified that the code complies with the projects coding standards.

[jrfnl]

@fredden Thank you for this PR. Really happy to see tests for this part of the code base being added.

I've gone through the file with a fine toothcomb and left a number of nitpick comments, but also some functional questions.

Hope this helps for the next iteration.

[fredden]

@jrfnl, I think this is ready for another review now. When we're happier with the final delta, I can rewrite the history so there are fewer commits before this is merged in.

[jrfnl]

@fredden Thanks for the updates, looking much better!

The @return array<...> tags are outdated now you've added the test names, so they need an update again.

Other than that, just one remark to go and this is ready for merge.

[jrfnl]

@fredden Thanks for your work on this Dan! All good now as far as I'm concerned.

Re: your remark about tidying up the branch- what did you have in mind ? I could squash-merge the PR, unless you have a reason why you'd prefer otherwise ?

[fredden]

🎉 Yes. A squash-merge via GitHub is fine with me.
Thanks for your coaching here too @jrfnl.