add tests for the cookie named, and updates type

rb/lib/selenium/webdriver/common/manager.rb

@@ -65,7 +65,7 @@ def add_cookie(opts = {})
       # Get the cookie with the given name
       #
       # @param [String] name the name of the cookie
-      # @return [Hash, nil] the cookie, or nil if it wasn't found.
+      # @return [Hash, nil] the cookie, or throws a NoSuchCookieError if it wasn't found.
       #
 
       def cookie_named(name)

rb/sig/lib/selenium/webdriver/common/manager.rbs

@@ -11,7 +11,7 @@ module Selenium
 
       def add_cookie: (?Hash[Symbol, untyped] opts) -> void
 
-      def cookie_named: (String name) -> Hash[Symbol, untyped]
+      def cookie_named: (String name) -> (Hash[Symbol, untyped] | Error::NoSuchCookieError)
 
       def delete_cookie: (String name) -> String
 
@@ -33,7 +33,7 @@ module Selenium
 
       def strip_port: (String str) -> String?
 
-      def convert_cookie: (Hash[String, untyped] cookie) -> Hash[Symbol, untyped]
+      def convert_cookie: (String) -> (Hash[Symbol, untyped] | Error::NoSuchCookieError)
     end
   end
 end

rb/spec/integration/selenium/webdriver/manager_spec.rb

@@ -248,6 +248,11 @@ module WebDriver
           driver.manage.delete_all_cookies
           expect(driver.manage.all_cookies).to be_empty
         end
+
+        it 'throws error when fetching non-existent cookie' do
+          expect { driver.manage.cookie_named('non-existent') }
+            .to raise_exception(Error::NoSuchCookieError)
+        end
       end
     end # Options
   end # WebDriver