Comment 15 for bug 1637601

The previous comment mentions a test-case and pattern, which were missing.
Here they are:

Test-case
===

Package is not installed -- no libvirt-qemu user/group:
---

# getent passwd libvirt-qemu
#

# getent group libvirt-qemu
#

Package is installed -- libvirt-qemu user/group is created w/ allocated uid/gid:
---

# dpkg -i libvirt{-bin,0}_1.3.1-1ubuntu10.5uidgid1_*.deb

# getent passwd libvirt-qemu
libvirt-qemu:x:64055:117:Libvirt Qemu,,,:/var/lib/libvirt:/bin/false

# getent group libvirt-qemu
libvirt-qemu:x:64055:libvirt-qemu

Package is uninstalled -- libvirt-qemu user/group is removed:
---

# apt-get --yes purge libvirt-bin

# getent passwd libvirt-qemu
#

# getent group libvirt-qemu
#

Package is installed with uid/gid taken -- libvirt-qemu user/group is created with other uid/gid:
---

# useradd --uid 64055 testuser
# groupadd --gid 64055 testgroup

# dpkg -i libvirt{-bin,0}_1.3.1-1ubuntu10.5uidgid1_*.deb
# echo $?
0

# getent passwd libvirt-qemu
libvirt-qemu:x:113:117:Libvirt Qemu,,,:/var/lib/libvirt:/bin/false

# getent group libvirt-qemu
libvirt-qemu:x:118:libvirt-qemu