chore: add some more tests to scanner

[danvk]

I played around with making this less class-based, but really it's not that much different. Just dropping this and replacing all the methods with closures. (Stashed in the functional-scanner on my laptop.)

[github-actions]

PR Compliance Checks

Thank you for your Pull Request! We have run several checks on this pull request in order to make sure it's suitable for merging into this project. The results are listed in the following section.

Issue Reference

In order to be considered for merging, the pull request description must refer to a specific issue number. This is described in our Contributing Guide. We are closing this pull request for now but you can update the pull request description and reopen the pull request.
The check is looking for a phrase similar to: "Fixes #XYZ" or "Resolves #XYZ" where XYZ is the issue number that this PR is meant to address.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ed5c79a) 74.92% compared to head (5b022a1) 83.08%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #4      +/-   ##
==========================================
+ Coverage   74.92%   83.08%   +8.15%     
==========================================
  Files           5        5              
  Lines         331      331              
  Branches       39       45       +6     
==========================================
+ Hits          248      275      +27     
+ Misses         82       55      -27     
  Partials        1        1              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.