Preload browser driver_path for system testing

The webdrivers gem configures Selenium::WebDriver::Service.driver_path
as a proc which updates the web drivers and returns their path.

This commit introduces SystemTesting::Browser#preload, which runs this
proc early. This ensures that webdrivers update is run before forking
for parallel testing, but doesn't explicitly tie us to that gem (and I
think anything configured as driver_path probably makes sense to
eager-load).

3 files changed, 16 insertions, 0 deletions

diff --git a/actionpack/lib/action_dispatch/system_test_case.rb b/actionpack/lib/action_dispatch/system_test_case.rb
index a7fb5fa330..29864c0f8e 100644
--- a/actionpack/lib/action_dispatch/system_test_case.rb
+++ b/actionpack/lib/action_dispatch/system_test_case.rb
@@ -4,6 +4,7 @@ gem "capybara", ">= 2.15"
 
 require "capybara/dsl"
 require "capybara/minitest"
+require "selenium/webdriver"
 require "action_controller"
 require "action_dispatch/system_testing/driver"
 require "action_dispatch/system_testing/browser"
diff --git a/actionpack/lib/action_dispatch/system_testing/browser.rb b/actionpack/lib/action_dispatch/system_testing/browser.rb
index c34907b6cb..f5f195d876 100644
--- a/actionpack/lib/action_dispatch/system_testing/browser.rb
+++ b/actionpack/lib/action_dispatch/system_testing/browser.rb
@@ -39,6 +39,19 @@ module ActionDispatch
           end
       end
 
+      # driver_path can be configured as a proc. The webdrivers gem uses this
+      # proc to update web drivers. Running this proc early allows us to only
+      # update the webdriver once and avoid race conditions when using
+      # parallel tests.
+      def preload
+        case type
+        when :chrome
+          ::Selenium::WebDriver::Chrome::Service.driver_path.try(:call)
+        when :firefox
+          ::Selenium::WebDriver::Firefox::Service.driver_path.try(:call)
+        end
+      end
+
       private
         def headless_chrome_browser_options
           capabilities.args << "--headless"
diff --git a/actionpack/lib/action_dispatch/system_testing/driver.rb b/actionpack/lib/action_dispatch/system_testing/driver.rb
index 25a09dd918..15943a55ea 100644
--- a/actionpack/lib/action_dispatch/system_testing/driver.rb
+++ b/actionpack/lib/action_dispatch/system_testing/driver.rb
@@ -9,6 +9,8 @@ module ActionDispatch
         @screen_size = options[:screen_size]
         @options = options[:options]
         @capabilities = capabilities
+
+        @browser.preload
       end
 
       def use