Replying to Ryan J Ollos:
Also modified TicketSystem.reset_ticket_fields to clear the cached property custom_fields, which was an issue discovered after writing the test.
It looks like this isn't needed outside of test execution since the environment is recreated when the trac.ini file contents change. Changing the [ticket-custom] definition will therefore result in recomputing the cached ticket fields and custom fields.
In the test case I'll just explicitly del TicketSystem(self.env).custom_fields.
