Set capybara as the default host in system specs

See:
rails/rails@ea77dbf#diff-ff5f366a442b8761d35f94807700fa77R162

Author: JonRowe

lib/rspec/rails/example/system_example_group.rb

@@ -101,9 +101,12 @@ def driven_by(driver, **driver_options, &blk)
 
         before do
           @routes = ::Rails.application.routes
+          @original_host = default_url_options[:host]
+          default_url_options.merge!(host: Capybara.app_host)
         end
 
         after do
+          default_url_options.merge!(host: @original_host)
           orig_stdout = $stdout
           $stdout = StringIO.new
           begin

spec/rspec/rails/example/system_example_group_spec.rb

@@ -29,6 +29,40 @@ module RSpec::Rails
       end
     end
 
+    describe 'rails url helpers' do
+      it 'have the rails system test default host' do
+        full_url = nil
+        group = RSpec::Core::ExampleGroup.describe do
+          include SystemExampleGroup
+
+          specify do
+            @routes.draw { get "/" => "page#index", as: :root }
+            full_url = root_url
+          end
+        end
+        group.run(failure_reporter)
+        expect(failure_reporter.exceptions).to eq []
+        expect(full_url).to match a_string_including(ActionDispatch::SystemTesting::TestHelpers::SetupAndTeardown::DEFAULT_HOST)
+      end
+    end
+
+    describe '#url_options' do
+      it 'has the rails system test default host' do
+        rails_url_options = {}
+        group = RSpec::Core::ExampleGroup.describe do
+          include SystemExampleGroup
+
+          specify { rails_url_options.merge!(url_options) }
+        end
+        group.run(failure_reporter)
+        expect(failure_reporter.exceptions).to eq []
+
+        expect(
+          rails_url_options
+        ).to match hash_including(host: ActionDispatch::SystemTesting::TestHelpers::SetupAndTeardown::DEFAULT_HOST)
+      end
+    end
+
     describe '#driver' do
       it 'uses :selenium driver by default' do
         group = RSpec::Core::ExampleGroup.describe do