Duplicable test is looking fine now.

activesupport/test/core_ext/duplicable_test.rb

@@ -4,22 +4,27 @@
 require 'active_support/core_ext/numeric/time'
 
 class DuplicableTest < Test::Unit::TestCase
-  NO  = [nil, false, true, :symbol, 1, 2.3, BigDecimal.new('4.56'), Class.new, Module.new, 5.seconds]
+  RAISE_DUP  = [nil, false, true, :symbol, 1, 2.3, BigDecimal.new('4.56'), 5.seconds]
   YES = ['1', Object.new, /foo/, [], {}, Time.now]
+  NO = [Class.new, Module.new]
 
   def test_duplicable
-    NO.each do |v|
+    (RAISE_DUP + NO).each do |v|
       assert !v.duplicable?
-      begin
-        v.dup
-        fail
-      rescue Exception
-      end
     end
 
     YES.each do |v|
       assert v.duplicable?
+    end
+
+    (YES + NO).each do |v|
       assert_nothing_raised { v.dup }
     end
+
+    RAISE_DUP.each do |v|
+      assert_raises(TypeError) do
+        v.dup
+      end
+    end
   end
 end