/testfor command does not work as it should

I apologize if this is a duplicate.

I was working on a project in one of my worlds. I added a dummy scoreboard objective, and made sure my value was set to 0. Then I put down 10 command blocks with comparators as the output that tested for the values 1-10. When I powered them, every single comparator lit up, even though my value was set at 0. There were no typos in any of the command blocks. I also tried changing my value to one of the tested for values, but still, all of the comparators lit up.

Commands used:

scoreboard objectives add days dummy Days
scoreboard players set @a days 0
testfor @r[score_days=1]
testfor @r[score_days=2]
testfor @r[score_days=3]
testfor @r[score_days=4]
testfor @r[score_days=5]
testfor @r[score_days=6]
testfor @r[score_days=7]
testfor @r[score_days=8]
testfor @r[score_days=9]
testfor @r[score_days=10]

What I expected to happen was:
None of the comparators would light up, as none of the command blocks tested for my value.

What actually happened was:
All of the comparators lit up.

Steps to reproduce:
1. Create a dummy scoreboard objective
2. Set your value to any number
3. Put down command blocks with comparators that test for your number and other values
4. Power all of them