Refactor "exposed" @system_dir instance variable

Author: pvdb

test/helper.rb

@@ -91,17 +91,17 @@ def ignore_deprecations
   end
 
   def rake_system_dir
-    @system_dir = "system"
+    system_dir = "system"
 
-    FileUtils.mkdir_p @system_dir
+    FileUtils.mkdir_p system_dir
 
-    File.write File.join(@system_dir, "sys1.rake"), <<~SYS
+    File.write File.join(system_dir, "sys1.rake"), <<~SYS
       task "sys1" do
         puts "SYS1"
       end
     SYS
 
-    ENV["RAKE_SYSTEM"] = @system_dir
+    ENV["RAKE_SYSTEM"] = system_dir
   end
 
   def rakefile(contents)

test/test_rake_application.rb

@@ -338,7 +338,7 @@ def test_load_from_system_rakefile
       load_rakefile
     end
 
-    assert_equal @system_dir, @app.system_dir
+    assert_equal "system", @app.system_dir
     assert_nil @app.rakefile
   rescue SystemExit
     flunk "failed to load rakefile"