Fixes FeedService tests to actually test things.

The original tests stubbed the private methods which means they mostly
just tested ruby's precedence order. :) Private methods are forced
integrations... we have to allow them to operate in turn in order to
assess behavior.
Removing TestHelper from FeedService tests.

This removes the overhead imprint.

Tests run at quick speed:

$ rake test:file[test/services/feed_service_test.rb]
test/services/feed_service_test.rb
Rack::File headers parameter replaces cache_control after Rack 1.5.
Run options: --seed 41627

.....

Finished tests in 0.015902s, 314.4225 tests/s, 377.3070 assertions/s.
Merge remote-tracking branch 'wilkie/bugfix/feed-service-tests'