core/Tracker/* Some code is being unit tested, but no test cover the full interactions and code path, eg. tracking a page, tracking a goal, setting a custom page name, etc.
Archiving. Archiving is not unit tested at the moment. The cheaper approach might be to test directly the data returned by APIs in a "black box" fashion, ie. replay "golden" logs to the tracker script, and check that we get expected API results. Each test would contain a small gold log testing a specific code path, as well as the expected reports from this log (visits, list of pages, list of referers, etc.)