Laravel Redis Facade Testing

I have a block of code in my Laravel 5 project which uses the Redis facade which I'd like to test. The code is part of a trait and structure is basically

private function getAgentArray(): ?array
{
    try {
        $key = Request::agentId();

        return Redis::exists($key) ? json_decode(Redis::get($key), true) : null;
    } catch (\Exception $e) {
        Log::debug($e->getMessage());

        return null;
    }
}

The function should provide an array of data for use internally in any classes which use the trait.

Is there a way I can mock this so that its output would be available for the class using the trait?. Basically I'm looking for getAgentArray() to return a fake array when called. I can't mock this directly as it's private so needs to be through the Redis facade if that's possible.

via Chebli Mohamed