NoMethodError: undefined method `edit_detailed_reservation_path' while running unit/application_helper_test.rb

Question

We are migrating 2.3.18 application to 3.2.x. We are facing an issue while running a test where it is not able to find routes using route helpers

Here is the assertion where we are facing issue

#test/unit/application_helper_test.rb
def test_calendar_link_to_with_named_route
  . . .
  calendar_link_to(31, date, {:named_route => 'edit_detailed_reservation_path', :method => :post})
  . . .
end

Here is how the method is defined in ApplicationHelper

def calendar_link_to(anchor_text, date, *args)
  options = args.first.is_a?(Hash) ? args.pop : {}
  method = options[:method]
  named_route = options[:named_route]

  url_hash = { :day => date.day, :month => date.month, :year => date.year }
  url = named_route ? self.send(named_route, url_hash) : url_hash

  link_options = { :id => "date-#{date.year}-#{date.month}-#{date.day}" }
  if date > Parameter.event_horizon
    link_options[:title] = 'This date is beyond the event horizon.'
  end
  link_options[:method] = method if method
  link_to(anchor_text, url, link_options)
end

While running the test we get following error

NoMethodError: undefined method `edit_detailed_reservation_path'

To resolve this error I have also tried to put the below line inside application_helper.rb

include Rails.application.routes.url_helpers

We use below command to run the test

rake test TEST=test/unit/application_helper_test.rb

In Rails 2, edit_detailed_reservation_path gives absolute URL while inspecting it in a pry session but same doesn't work in Rails 3.

Would anybody please guide us what could be the issue and how to fix it?