class_attribute gets instance methods which delegate to but may override their class values as you'd expect. Disable instance writer methods with :instance_writer => false.

1 files changed, 25 insertions, 10 deletions

diff --git a/activesupport/test/core_ext/class/attribute_test.rb b/activesupport/test/core_ext/class/attribute_test.rb
index ef84b9f255..06b4cf075f 100644
--- a/activesupport/test/core_ext/class/attribute_test.rb
+++ b/activesupport/test/core_ext/class/attribute_test.rb
@@ -2,13 +2,6 @@ require 'abstract_unit'
 require 'active_support/core_ext/class/attribute'
 
 class ClassAttributeTest < ActiveSupport::TestCase
-  class Base
-    class_attribute :setting
-  end
-
-  class Subclass < Base
-  end
-
   def setup
     @klass = Class.new { class_attribute :setting }
     @sub = Class.new(@klass)
@@ -40,8 +33,30 @@ class ClassAttributeTest < ActiveSupport::TestCase
     assert_equal true, @klass.setting?
   end
 
-  test 'no instance delegates' do
-    assert_raise(NoMethodError) { @klass.new.setting }
-    assert_raise(NoMethodError) { @klass.new.setting? }
+  test 'instance reader delegates to class' do
+    assert_nil @klass.new.setting
+
+    @klass.setting = 1
+    assert_equal 1, @klass.new.setting
+  end
+
+  test 'instance override' do
+    object = @klass.new
+    object.setting = 1
+    assert_nil @klass.setting
+    @klass.setting = 2
+    assert_equal 1, object.setting
+  end
+
+  test 'instance query' do
+    object = @klass.new
+    assert_equal false, object.setting?
+    object.setting = 1
+    assert_equal true, object.setting?
+  end
+
+  test 'disabling instance writer' do
+    object = Class.new { class_attribute :setting, :instance_writer => false }.new
+    assert_raise(NoMethodError) { object.setting = 'boom' }
   end
 end