Comment 62 for bug 1717040

a) compression tests - artful - PASS
starting with the original artful packages:
ubuntu@artful-zstd:~$ dpkg -l|grep zstd
ii libzstd1 1.3.1+dfsg-1 amd64 fast lossless compression algorithm
ii zstd 1.3.1+dfsg-1 amd64 fast lossless compression algorithm -- CLI tool

ubuntu@artful-zstd:~$ zstd /usr/bin/snap -o snap.1.3.1.zst
/usr/bin/snap : 31.03% (11318760 => 3512707 bytes, snap.1.3.1.zst)

gives:
-rwxr-xr-x 1 ubuntu ubuntu 3.4M Nov 30 16:42 snap.1.3.1.zst

Now upgrading to the package in proposed:
The following additional packages will be installed:
  libzstd1
The following packages will be upgraded:
  libzstd1 zstd
...
Get:1 http://br.archive.ubuntu.com/ubuntu artful-proposed/universe amd64 zstd amd64 1.3.1+dfsg-1ubuntu0.1 [238 kB]
Get:2 http://br.archive.ubuntu.com/ubuntu artful-proposed/universe amd64 libzstd1 amd64 1.3.1+dfsg-1ubuntu0.1 [152 kB]
...

Compressing with the new package:
ubuntu@artful-zstd:~$ zstd /usr/bin/snap -o snap.1.3.1-updated.zst
/usr/bin/snap : 31.03% (11318760 => 3512707 bytes, snap.1.3.1-updated.zst)

Decompressing the previous one:
ubuntu@artful-zstd:~$ zstd -d snap.1.3.1.zst -o snap.1.3.1
snap.1.3.1.zst : 11318760 bytes

Decompressing the updated one:
ubuntu@artful-zstd:~$ zstd -d snap.1.3.1-updated.zst -o snap.1.3.1-updated
snap.1.3.1-updated.zst: 11318760 bytes

MD5 of everything:
ubuntu@artful-zstd:~$ md5sum /usr/bin/snap snap.1.3.1 snap.1.3.1-updated
0b65998bc775d444b2ee7d00cd18634a /usr/bin/snap
0b65998bc775d444b2ee7d00cd18634a snap.1.3.1
0b65998bc775d444b2ee7d00cd18634a snap.1.3.1-updated

Downgrading back to the original artful version:
ubuntu@artful-zstd:~$ sudo apt install zstd=1.3.1+dfsg-1 libzstd1=1.3.1+dfsg-1
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be DOWNGRADED:
  libzstd1 zstd

Decompressing and another md5 snapshot:
ubuntu@artful-zstd:~$ zstd -d snap.1.3.1.zst -o snap.1.3.1-new
snap.1.3.1.zst : 11318760 bytes
ubuntu@artful-zstd:~$ md5sum snap.1.3.1-new /usr/bin/snap
0b65998bc775d444b2ee7d00cd18634a snap.1.3.1-new
0b65998bc775d444b2ee7d00cd18634a /usr/bin/snap