rails host in rspec feature test

I have a rails app with a feature spec that verify page url after user login expect(page.current_url).to eq(posts_url).

I configure Capybara host in spec/spec_helper.rb like this

config.before(:each) do
  Capybara.app_host = "http://mydomain.dev"
end

Test fail with note:

expected: "http://ift.tt/UqzmSA"
      got: "http://ift.tt/1F9dDPH"

I configure rails hosts with Rails.application.routes.default_url_options[:host] = 'mydomain.dev' but is seems it doesn't work properly (my tests still fails)