Dedupe and simplify standard_system_dir

lib/rake/application.rb

@@ -754,12 +754,10 @@ def system_dir # :nodoc:
     end
 
     # The standard directory containing system wide rake files.
-    if Win32.windows?
-      def standard_system_dir #:nodoc:
+    def standard_system_dir #:nodoc:
+      if windows?
         File.join(Dir.home, "Rake")
-      end
-    else
-      def standard_system_dir #:nodoc:
+      else
         File.join(Dir.home, ".rake")
       end
     end

test/test_rake_application.rb

@@ -365,6 +365,44 @@ def @app.standard_system_dir
     flunk "failed to find system rakefile"
   end
 
+  def test_load_from_calculated_system_rakefile_on_windows
+    rakefile_default
+    def @app.windows?
+      true
+    end
+
+    @app.instance_eval do
+      handle_options []
+      options.silent = true
+      options.load_system = true
+      options.rakelib = []
+      load_rakefile
+    end
+
+    assert_equal File.join(Dir.home, "Rake"), @app.system_dir
+  rescue SystemExit
+    flunk "failed to find system rakefile"
+  end
+
+  def test_load_from_calculated_system_rakefile_on_unix
+    rakefile_default
+    def @app.windows?
+      false
+    end
+
+    @app.instance_eval do
+      handle_options []
+      options.silent = true
+      options.load_system = true
+      options.rakelib = []
+      load_rakefile
+    end
+
+    assert_equal File.join(Dir.home, ".rake"), @app.system_dir
+  rescue SystemExit
+    flunk "failed to find system rakefile"
+  end
+
   def test_terminal_columns
     old_rake_columns = ENV["RAKE_COLUMNS"]