public function addMigration(string $module, string $path)
    {
        $module = self::normalizeModule($module);
        if (isset($this->modules[$module]))
            throw new MigrationException("Duplicate module: " . $module);

        $instance = new Module($module, $path, $this->db);
        $this->modules[$module] = $instance;
        return $instance;
    }