How do you keep your phone vibrating indefinitely?

I'm suspecting that the vibrator in my phone is not working properly. Before opening the case, I'd like to diagnose first. I need to make my phone keep vibrating for a while, say, like 2 minutes or more. I haven't found any good solution other than calling this phone with another. I'd like to keep it vibrating without generating other sound, e.g. ringtone when someone calls you.