Call system test driver per-instance rather than globally

Previously the system test subclasses would call `driven_by` when the
app booted and not again when the test was initialized which resulted in
the driver from whichever class was called last to be used in tests.

In rails/rails#28144 the `driven_by` method was changed to run `use` on
setup and `reset` on teardown. While this was a viable fix this really
pointed to the problem that system test `driven_by` was a global
setting, rather than a per-class setting.

To alieviate this problem calling the driver should be done on an
instance level, rather than on the global level. I added an `initialize`
method to `SystemTestCase` which will call `use` on the superclass
driver. Running the server has been moved to `start_application` so that
it only needs to be called once on boot and no options from `driven_by`
were being passed to it.

This required a largish rewrite of the tests. Each test needs to utilize
the subclass so that it can properly test the drivers.
`ActionDispatch::SystemTestCase` shouldn't be called directly anymore.

3 files changed, 13 insertions, 11 deletions

diff --git a/actionpack/lib/action_dispatch/system_test_case.rb b/actionpack/lib/action_dispatch/system_test_case.rb
index d872fca6bf..1bf47d2556 100644
--- a/actionpack/lib/action_dispatch/system_test_case.rb
+++ b/actionpack/lib/action_dispatch/system_test_case.rb
@@ -83,12 +83,19 @@ module ActionDispatch
     include SystemTesting::TestHelpers::SetupAndTeardown
     include SystemTesting::TestHelpers::ScreenshotHelper
 
+    def initialize(*) # :nodoc:
+      super
+      self.class.superclass.driver.use
+    end
+
     def self.start_application # :nodoc:
       Capybara.app = Rack::Builder.new do
         map "/" do
           run Rails.application
         end
       end
+
+      SystemTesting::Server.new.run
     end
 
     # System Test configuration options
@@ -104,12 +111,12 @@ module ActionDispatch
     #
     #   driven_by :selenium, screen_size: [800, 800]
     def self.driven_by(driver, using: :chrome, screen_size: [1400, 1400])
-      driver = SystemTesting::Driver.new(driver, using: using, screen_size: screen_size)
-
-      setup { driver.use }
-      teardown { driver.reset }
+      @driver = SystemTesting::Driver.new(driver, using: using, screen_size: screen_size)
+    end
 
-      SystemTesting::Server.new.run
+    # Returns the driver object for the initialized system test
+    def self.driver
+      @driver ||= SystemTestCase.driven_by(:selenium)
     end
   end
 
diff --git a/actionpack/lib/action_dispatch/system_testing/driver.rb b/actionpack/lib/action_dispatch/system_testing/driver.rb
index 65e43d3584..72d132d64f 100644
--- a/actionpack/lib/action_dispatch/system_testing/driver.rb
+++ b/actionpack/lib/action_dispatch/system_testing/driver.rb
@@ -12,10 +12,6 @@ module ActionDispatch
         setup
       end
 
-      def reset
-        Capybara.current_driver = @current
-      end
-
       private
         def selenium?
           @name == :selenium
@@ -31,7 +27,6 @@ module ActionDispatch
 
         def setup
           Capybara.current_driver = @name
-          @current = Capybara.current_driver
         end
     end
   end
diff --git a/actionpack/lib/action_dispatch/system_testing/test_helpers/screenshot_helper.rb b/actionpack/lib/action_dispatch/system_testing/test_helpers/screenshot_helper.rb
index e37f6d02aa..6de8fb74dc 100644
--- a/actionpack/lib/action_dispatch/system_testing/test_helpers/screenshot_helper.rb
+++ b/actionpack/lib/action_dispatch/system_testing/test_helpers/screenshot_helper.rb
@@ -57,7 +57,7 @@ module ActionDispatch
           end
 
           def supports_screenshot?
-            page.driver.public_methods(false).include?(:save_screenshot)
+            Capybara.current_driver != :rack_test
           end
       end
     end