I am attempting to make it easier to test Rails engines.
It's helpful that `Rails.application.routes.url_helpers` responds to
URL helper methods both on itself or if it's included in a class:
> Rails.application.routes.url_helpers.root_path => "/" > class Foo include Rails.application.routes.url_helpers end => Foo > Foo.new.root_path => "/"
`MountedHelpers`, which stores helpers for mounted engines, does not
do a similar thing ... as demonstrated by the `NoMethodError`:
> Rails.application.routes.mounted_helpers.railsengine NoMethodError: undefined method `railsengine' for ActionDispatch::Routing::RouteSet::MountedHelpers:Module from (pry):20:in `block (2 levels) in <top (required)>' > class Foo include Rails.application.routes.mounted_helpers end => Foo > Foo.new.railsengine #<ActionDispatch::Routing::RoutesProxy:0x007fc86e85c6c0 @routes=#<ActionDispatch::Routing::RouteSet:0x007fc869c31e80>, @scope=... >
Would you welcome a pull request to `extend self` in `MountedHelpers`
so it could be delegated directly to?
Then, in a test harness (for instance, in an RSpec routing spec), we
could delegate directly to `MountedHelpers`. Otherwise, we'd have to
construct an object solely to hold the mounted helpers. The setup for
this might be pretty awkward.