Add test select_tag escapes prompt

actionpack/test/template/form_tag_helper_test.rb

@@ -213,6 +213,12 @@ def test_select_tag_with_prompt
     assert_dom_equal expected, actual
   end
 
+  def test_select_tag_escapes_prompt
+    actual = select_tag "places", "<option>Home</option><option>Work</option><option>Pub</option>".html_safe, :prompt => "<script>alert(1337)</script>"
+    expected = %(<select id="places" name="places"><option value="">&lt;script&gt;alert(1337)&lt;/script&gt;</option><option>Home</option><option>Work</option><option>Pub</option></select>)
+    assert_dom_equal expected, actual
+  end
+
   def test_select_tag_with_prompt_and_include_blank
     actual = select_tag "places", "<option>Home</option><option>Work</option><option>Pub</option>".html_safe, :prompt => "string", :include_blank => true
     expected = %(<select name="places" id="places"><option value="">string</option><option value=""></option><option>Home</option><option>Work</option><option>Pub</option></select>)