simple_form with rspec requires default_url_options to be set

[Koen.]

When converting my forms from regular `form_for` to `simple_form_for` I ran into my specs errored with the following:

 ActionView::Template::Error:

        Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or set :only_path to true

Now it turns out this can be quite easily fixed by adding this to my rspec helpers:

Rails.application.routes.default_url_options[:host] = 'test.host'

Although I don't understand why simple_form requires this, because when using regular form helpers it isn't required.