If you try to use

/testfor @p[Score_name=x,Score_name_Min=x]

it will list everyone instead of someone with exactly x like it should. Here you can see me using it to test for people with over full health and since I am the only person on and have only full health it should not say my name in the results. If you can't read it that well, the command I am using is

/testfor @p[Score_health=500,Score_health_Min=500]