@Test(expected = IllegalStateException.class)
public void testAdd_MultipleDocumentsForOneId() {

    IdAddingSolrUpdateWriter updateWriter = new IdAddingSolrUpdateWriter(
            UNIQUE_KEY_FIELD, DOCUMENT_ID, null, TABLE_NAME, updateCollector);
    
    updateWriter.add(solrDoc);
    updateWriter.add(solrDoc);
}