using set full_path in test mode too

Here is my take on the issue https://github.com/intridea/omniauth/issues/656. But I lack the detailed understanding of Rack to fix the failing test. Maybe you or someone else knows the solution right away.

    OmniAuth::Strategy setup phase when options[:setup] = true calls through to /auth/:provider/setup
     Failure/Error: strategy.call(make_env('/auth/test'))
     NoMethodError:
       undefined method `+' for nil:NilClass
     # ./lib/omniauth/strategy.rb:404:in `full_host'
     # ./lib/omniauth/strategy.rb:271:in `mock_request_call'
     # ./lib/omniauth/strategy.rb:256:in `mock_call!'
     # ./lib/omniauth/strategy.rb:171:in `call!'