Add support for ferrum as a driver

lib/teaspoon/driver.rb

@@ -13,3 +13,4 @@ module Driver
 Teaspoon::Driver.register(:phantomjs, "Teaspoon::Driver::Phantomjs", "teaspoon/driver/phantomjs", default: true)
 Teaspoon::Driver.register(:selenium, "Teaspoon::Driver::Selenium", "teaspoon/driver/selenium")
 Teaspoon::Driver.register(:browserstack, "Teaspoon::Driver::BrowserStack", "teaspoon/driver/browserstack")
+Teaspoon::Driver.register(:ferrum, "Teaspoon::Driver::Ferrum", "teaspoon/driver/ferrum")

lib/teaspoon/driver/ferrum.rb

@@ -0,0 +1,50 @@
+# :nocov:
+begin
+  require "ferrum"
+rescue LoadError
+  Teaspoon.abort("Could not find Ferrum. Install the ferrum gem.")
+end
+# :nocov:
+
+require "teaspoon/driver/base"
+
+module Teaspoon
+  module Driver
+    class Ferrum < Base
+      def initialize(options = nil)
+        options ||= {}
+        case options
+        when Hash then @options = options
+        when String then @options = JSON.parse(options)
+        else raise Teaspoon::DriverOptionsError.new(types: "hash or json string")
+        end
+      rescue JSON::ParserError
+        raise Teaspoon::DriverOptionsError.new(types: "hash or json string")
+      end
+
+      def run_specs(runner, url)
+        driver = ::Ferrum::Browser.new(driver_options)
+        driver.go_to(url)
+
+        if driver.evaluate("window.Teaspoon")
+          until driver.evaluate("window.Teaspoon.finished")
+            sleep 0.01
+          end
+          driver.evaluate("window.Teaspoon.getMessages() || []").each do |line|
+            runner.process("#{line}\n")
+          end
+        end
+      ensure
+        driver.quit if driver
+      end
+
+      protected
+
+        def driver_options
+          @driver_options ||= HashWithIndifferentAccess.new(
+            timeout: Teaspoon.configuration.driver_timeout.to_i
+          ).merge(@options)
+        end
+    end
+  end
+end