message: More rigorous.
diff: --TEST--
  -swoole_coroutine: mysql prepare (select)
  +swoole_coroutine: mysql prepare (destruct)
  --SKIPIF--
  <?php require __DIR__ . '/../include/skipif.inc'; ?>
  --FILE--
  @@ -11,14 +11,16 @@ use Swoole\Coroutine as co;
  co::create(function () {
  $db = new co\MySQL();
  - $server = array(
  + $server = [
  'host' => MYSQL_SERVER_HOST,
  'user' => MYSQL_SERVER_USER1,
  'password' => MYSQL_SERVER_PWD,
  'database' => MYSQL_SERVER_DB1,
  - );
  + ];
  $ret1 = $db->connect($server);
  +
  + $start_prepared_num = (int)(($db->query('show status like \'Prepared_stmt_count\''))[0]['Value']);
  if (!$ret1) {
  echo "CONNECT ERROR\n";
  return;
  @@ -38,12 +40,13 @@ co::create(function () {
  echo "PREPARE3 ERROR\n";
  return;
  }
  - $prepared_num = (int)(($db->query('show status like \'Prepared_stmt_count\''))[0]['Value']);
  - assert($prepared_num === 3);
  - $stmt1 = null;
  - unset($stmt2);
  - $prepared_num = (int)(($db->query('show status like \'Prepared_stmt_count\''))[0]['Value']);
  - assert($prepared_num === 1);
  +
  + $prepared_num1 = (int)(($db->query('show status like \'Prepared_stmt_count\''))[0]['Value']);
  + assert($prepared_num1 - $start_prepared_num === 3);
  + $stmt1 = null; //destruct
  + unset($stmt2); //destruct
  + $prepared_num2 = (int)(($db->query('show status like \'Prepared_stmt_count\''))[0]['Value']);
  + assert($prepared_num1 - $prepared_num2 === 2);
  });
  ?>
  