From the discussion in https://gerrit.wikimedia.org/r/c/mediawiki/services/parsoid/+/507868
Testing is hampered by the ApiHelper calling the production api rather than the mock, so we're getting different file information.
Fixing that probably belongs in a dep or follow up anyways.
This testing bit is related to https://gerrit.wikimedia.org/r/c/mediawiki/services/parsoid/+/513529/19/src/Wt2Html/TT/TemplateHandler.php#885 .. so, whatever solution it is should handle it all together.
For testing template handler code there, I pass offline mode over to the PHP scripts. Otherwise, I have the same problem of getting information from the live API, not the mock API.