The fallback functionality of the themes is good, but it is resource intensive if something is really really missing from a theme. For example, a user might make a custom theme for their OPAC, specify a TT include, but not include it in their theme (intentionally, or accidentally). The process of looking through all of the themes to find the fallback causes very slow page loads for that page, we should have a test that theme creators can run to check for this circumstance.