assert_dom_equal"<div class=\"differentError\">beforecan't be emptyafter</div>",error_message_on(:post,:author_name,:css_class=>'differentError',:prepend_text=>'before',:append_text=>'after')
assert_dom_equal"<span class=\"differentError\">beforecan't be emptyafter</span>",error_message_on(:post,:author_name,:html_tag=>"span",:css_class=>'differentError',:prepend_text=>'before',:append_text=>'after')