Extend Test Coverage to Check Notes and Spans

[InsertCreativityHere]

Currently, most of our tests only check that the message/fields of a diagnostic are correct,
and neglect to check any additional context stored by the diagnostic (span, scope, or notes).

Testing these pieces of 'extra' information definitely isn't as important as testing the diagnostic's field & message,
but are probably worth testing none-the-less; otherwise we may be emitting bogus notes or incorrect snippets.