### Question:
RowAndFamilyAddingSolrUpdateWriter implements SolrUpdateWriter { @Override public void deleteById(String documentId) { delegateUpdateWriter.deleteById(documentId); } RowAndFamilyAddingSolrUpdateWriter(String rowField, String columnFamilyField,
            UniqueKeyFormatter uniqueKeyFormatter,
            KeyValue keyValue,SolrUpdateWriter delegateUpdateWriter); @Override void add(SolrInputDocument solrDocument); @Override void deleteById(String documentId); @Override void deleteByQuery(String query);  }### Answer:
@Test public void testDeleteById() { RowAndFamilyAddingSolrUpdateWriter updateWriter = new RowAndFamilyAddingSolrUpdateWriter("_row_", null, uniqueKeyFormatter, keyValue, delegateWriter); byte[] rowBytes = Bytes.toBytes("_row_"); doReturn("_rowkey_").when(uniqueKeyFormatter).formatRow(rowBytes); updateWriter.deleteById(uniqueKeyFormatter.formatRow(rowBytes)); verify(delegateWriter).deleteById("_rowkey_"); }