The libvirt system requires you to define any virtual machines before you can use them. While there are GUI tools to assist with this process, the portable and canonical method is to use an XML definition.
This config file is a minimal definition for a LXC system, with two key settings that would need to be changed to be used for multiple tests:
If you have been following the exmaple scripts, you will have a container root filesystem in the /var/lib/container-example/example1 sub-directory and can use this example file unedited with the following command:
virsh -c lxc:/// define libvirt-lxc-example1.xml