We can test hostgroup assignment in other tests if desired.

No need for a file on disk; it's only referenced once.

A lot of the testing doesn't really flex what a real icinga2 server does. We can implement a simple fake server with about 250 lines of Go, then we get all the benefits of really quick feedback and no dependency on an icinga2 server (which isn't super easy to set up) for most tests. More complicated tests are still performed against a real server listening on loopback (if available).

For some reason the API returns an internal server error status rather than a Not Found status (as in other methods in the API). We can catch the condition when results are empty and return ErrNoMatch.

This is a bit tricky. url.QueryEscape() encodes spaces in queries as "+", but Icinga2 wants them as "%20". A test case is included because this was kinda tricky to debug.

The check was incorrect before. The HTTP status on responses is still 200 OK, but with empty results if there are no matches to the filter.

This also adds a test for checking all hosts in a HostGroup.

And also add a icinga_test package that does the black-box tests i.e. tests which speak to a real icinga server.