I hooked up a hopper clock to a command block:

"scoreboard players set @a[score_player=0] player 1"

is in the command block and I set my score to 0 yet there is no response.
Also, I tried changing my player score to 1 and had a hopper clock to:

"testfor @a[score_player_min=1,score_player=1]"

and there is no output into my comparator!
There are multiple issues that are exactly like this one except all have been "resolved" and obviously it is NOT resolved.