if (!defined('CIVICRM_DSN')) {
  if (CIVICRM_UF === 'UnitTests' && isset($GLOBALS['_CV']['TEST_DB_DSN'])) {
    define('CIVICRM_DSN', $GLOBALS['_CV']['TEST_DB_DSN']);
  }
  else {
    define('CIVICRM_DSN', 'mysql://USERNAME:PASSWORD@DBHOSTNAME/DATABASENAME?new_link=true');
  }
}

if (!defined('CIVICRM_DSN')) {
  if (CIVICRM_UF === 'UnitTests' && isset($GLOBALS['_CV']['TEST_DB_DSN'])) {
    define('CIVICRM_DSN', $GLOBALS['_CV']['TEST_DB_DSN']);
  }
  else {
    define('CIVICRM_DSN', 'mysql://USERNAME:PASSWORD@DBHOSTNAME/DATABASENAME?new_link=true&useSSL=true&ssl-ca=(/etc/mysql/ssl/cacert.pem)&ssl-cert=(/etc/mysql/ssl/client-cert.pem)&ssl-key=(/etc/mysql/ssl/client-key.pem)');
  }
}

Initialization Error

Array
(
    [callback] => Array
        (
            [0] => CRM_Core_Error
            [1] => simpleHandler
        )

    [code] => -24
    [message] => DB Error: connect failed
    [mode] => 16
    [debug_info] =>  [nativecode=No such file or directory]
    [type] => DB_Error
    [user_info] =>  [nativecode=No such file or directory]
    [to_string] => [db_error: message="DB Error: connect failed" code=-24 mode=callback callback=CRM_Core_Error::simpleHandler prefix="" info=" [nativecode=No such file or directory]"]