How to mock request object for rspec helper tests?

This isn't a complete answer to your question, but for the record, you can mock a request using ActionController::TestRequest.new(). Something like:

describe ApplicationHelper do
  it "should prepend subdomain to host" do
    test_domain = 'xxxx:xxxx'
    controller.request = ActionController::TestRequest.new(:host => test_domain)
    helper.root_with_subdomain("test").should = "test.#{test_domain}"
  end
end

You have to prepend the helper method with 'helper':

describe ApplicationHelper do
  it "should prepend subdomain to host" do
    helper.root_with_subdomain("test").should = "test.xxxx:xxxx"
  end
end

Additionally to test behavior for different request options, you can access the request object throught the controller:

describe ApplicationHelper do
  it "should prepend subdomain to host" do
    controller.request.host = 'www.domain.com'
    helper.root_with_subdomain("test").should = "test.xxxx:xxxx"
  end
end

I had a similar problem, i found this solution to work:

before(:each) do
  helper.request.host = "yourhostandorport"
end