Add test to make sure that add two safe buffers always return a safe …

…buffer

activesupport/test/safe_buffer_test.rb

@@ -96,6 +96,13 @@ def setup
     assert !@buffer.dup.html_safe?
   end
 
+  test "Should return safe buffer when added with another safe buffer" do
+    clean = "<script>".html_safe
+    result_buffer = @buffer + clean
+    assert result_buffer.html_safe?
+    assert_equal "<script>", result_buffer
+  end
+
   test "Should raise an error when safe_concat is called on dirty buffers" do
     @buffer.gsub!('', '<>')
     assert_raise ActiveSupport::SafeBuffer::SafeConcatError do