def unlink_relation_between(topic, zoom_class, *relation_candidate_ids)
    topic = topic.id.to_s if topic.is_a?(Topic)
    item_checkbox_hash = item_checkbox_hash_from(relation_candidate_ids)
    post '/site/search/unlink_related', :relate_to_item => topic, :relate_to_type => 'Topic', :related_class => zoom_class, :item => item_checkbox_hash
    assert_response :redirect