Eris\TestTrait::withRand PHP Method

    protected function withRand($randFunction)
    {
        // TODO: invert and wrap rand, srand into objects?
        if ($randFunction instanceof \Eris\Random\RandomRange) {
            $this->randFunction = function ($lower = null, $upper = null) use($randFunction) {
                return $randFunction->rand($lower, $upper);
            };
            $this->seedFunction = function ($seed) use($randFunction) {
                return $randFunction->seed($seed);
            };
        }
        if (is_callable($randFunction)) {
            switch ($randFunction) {
                case 'rand':
                    $seedFunction = 'srand';
                    break;
                case 'mt_rand':
                    $seedFunction = 'mt_srand';
                    break;
                default:
                    throw new BadMethodCallException("When specifying random generators different from the standard ones, you must also pass a \$seedFunction callable that will be called to seed it.");
            }
            $this->randFunction = $randFunction;
            $this->seedFunction = $seedFunction;
        }
        return $this;
    }