Для CentOS 7.5 запустите от имени root:
cd /etc/yum.repos.d/
wget https://download.opensuse.org/repositories/systemsmanagement:Ardana:8:CentOS/CentOS_7.5/systemsmanagement:Ardana:8:CentOS.repo
yum install python-testtools
Для CentOS 7.3 запустите от имени root:
cd /etc/yum.repos.d/
wget https://download.opensuse.org/repositories/systemsmanagement:Ardana:8:CentOS/CentOS_7.3/systemsmanagement:Ardana:8:CentOS.repo
yum install python-testtools
Для CentOS 7 запустите от имени root:
cd /etc/yum.repos.d/
wget https://download.opensuse.org/repositories/systemsmanagement:Ardana:8:CentOS/CentOS_7/systemsmanagement:Ardana:8:CentOS.repo
yum install python-testtools