A number of test were defining and using the same controller
MyController = Class.new(ActionController::Base)
which was causing some state to leak across tests.
Fixes#870
Commit af81a40 introduced passing a serializer's 'options'
along to its associated model serializers.
Thus, an explicit 'each_serializer' passed to render for a
singular resource would be passed on as the implicit 'serializer'
for its associations.
With @bf4
