private function common($old, $new, $expected)
 {
     $ofs = new mock_output_file_segmenter();
     $old_schema = new SimpleXMLElement($old);
     $old_table = $old_schema->table;
     $new_schema = new SimpleXMLElement($new);
     $new_table = $new_schema->table;
     pgsql8_diff_tables::update_table_options($ofs, $ofs, $old_schema, $old_table, $new_schema, $new_table);
     $actual = trim($ofs->_get_output());
     $this->assertEquals($expected, $actual);
 }