fixes a test, and explains why AR::AttributeMethods checks defined?(@attributes) in some places

Author: fxn

activerecord/lib/active_record/attribute_methods.rb

@@ -172,6 +172,8 @@ def respond_to?(name, include_private = false)
 
       # If the result is true then check for the select case.
       # For queries selecting a subset of columns, return false for unselected columns.
+      # We check defined?(@attributes) not to issue warnings if called on objects that
+      # have been allocated but not yet initialized.
       if defined?(@attributes) && @attributes.present? && self.class.column_names.include?(name)
         return has_attribute?(name)
       end
@@ -340,6 +342,7 @@ def arel_attributes_with_values_for_update(attribute_names) # :nodoc:
     end
 
     def attribute_method?(attr_name) # :nodoc:
+      # We check defined? because Syck calls respond_to? before actually calling initialize.
       defined?(@attributes) && @attributes.include?(attr_name)
     end
 

activerecord/lib/active_record/core.rb

@@ -352,7 +352,9 @@ def connection_handler
 
     # Returns the contents of the record as a nicely formatted string.
     def inspect
-      inspection = if @attributes
+      # We check defined?(@attributes) not to issue warnings if the object is
+      # allocated but not initialized.
+      inspection = if defined?(@attributes) && @attributes
                      self.class.column_names.collect { |name|
                        if has_attribute?(name)
                          "#{name}: #{attribute_for_inspect(name)}"

activerecord/test/cases/attribute_methods_test.rb

@@ -141,13 +141,10 @@ def test_respond_to_with_allocated_object
     assert_respond_to topic, :title
   end
 
-  # IRB inspects the return value of "MyModel.allocate"
-  # by inspecting it.
+  # IRB inspects the return value of "MyModel.allocate".
   def test_allocated_object_can_be_inspected
     topic = Topic.allocate
-    topic.instance_eval { @attributes = nil }
-    assert_nothing_raised { topic.inspect }
-    assert topic.inspect, "#<Topic not initialized>"
+    assert_equal "#<Topic not initialized>", topic.inspect
   end
 
   def test_array_content