i gave myself a command block(command blocks where enabled) placed it down and entered this command: testfor @a[x=-505,y=57,z=-846,r=0]. then put a comparator infront of the command block with the testfor command and then put another command block infront of the comparator and entered in a tellraw command. i went to the coordinates and powered the testfor command block the comparator did not power and i went to check the output of the command block and there was no output

that I expected to happen was...:
the comparator would recieve power and power the other command block

What actually happened was...:
nothing really happend and there was no output of the command block

Steps to Reproduce:
1.enter a testfor command
2. go to the testfor coordinates
3. power command block