I'm concerned about the find behaviour when a template combination specifying *only* an environment or only a host group.  The tests below don't include that, they're for hosts without a host group or env being passed in (if the latter is possible) - they test that a host with only a hg matches a template_combination that only specifies a hg.

I don't see anything to test that a host with both hg + env (both passed into find_template) can match a template_combination specifying only one.