This seems like a small change (apart from all the
test changes), but it fundamentally changes how
the app finds "topic" on message objects. Now
all code that used to set "subject" now sets "topic"
on message-like objects. We convert incoming messages
to have topic, and we write to "topic" all the way up
to hitting the server (which now accepts "topic" on
incoming endpoints).
We fall back to subject as needed, but the code will
emit a warning that should be heeded--the "subject"
field is prone to becoming stale for things like
topic changes.
The goal here was to enforce 100% coverage on
parse_narrow, but the code has an unreachable line
and is overly tolerant of bogus urls. This will
be fixed in the next commit.
This run_test helper sets up a convention that allows
us to give really short tracebacks for errors, and
eventually we can have more control over running
individual tests. (The latter goal has some
complications, since we often intentionally leak
setup in tests.)