public static function getAssertionIdentifier($identifier = null)
    {
        // Keep a registry of how many assertions were run
        // in this test suite, and in this test
        $methodName = static::$suite->getName();
        static::$assertionsInTest[$methodName] = isset(static::$assertionsInTest[$methodName])
            ? static::$assertionsInTest[$methodName]
            : -1;

        $name = $methodName.'-'.++static::$assertionsInTest[$methodName];
        $name = $identifier ? $name.': '.$identifier : $name;

        return $name;
    }