class ConnectionFailureTest

class ConnectionFailureTest extends KernelTestBase {
    
    /**
     * {@inheritdoc}
     */
    protected static $modules = [
        'dblog',
    ];
    
    /**
     * Tests logging of connection failures.
     */
    public function testConnectionFailureLogging() {
        $this->installSchema('dblog', [
            'watchdog',
        ]);
        // MySQL errors like "1153 - Got a packet bigger than 'max_allowed_packet'
        // bytes" or "1100 - Table 'xyz' was not locked with LOCK TABLES" lead to a
        // database connection unusable for further requests. All further request
        // will result in a "2006 - MySQL server had gone away" error. As a
        // consequence it's impossible to use this connection to log the causing
        // initial error itself. Using Database::closeConnection() we simulate such
        // a corrupted connection. In this case dblog has to establish a different
        // connection by itself to be able to write the log entry.
        Database::closeConnection();
        // Create a log entry.
        $this->container
            ->get('logger.factory')
            ->get('php')
            ->error('testConnectionFailureLogging');
        // Re-establish the default database connection.
        $database = Database::getConnection();
        $query = $database->select('watchdog')
            ->condition('message', 'testConnectionFailureLogging');
        $query->addExpression('MAX([wid])');
        $wid = $query->execute()
            ->fetchField();
        $this->assertNotEmpty($wid, 'Watchdog entry has been stored in database.');
    }

}