Comment 59 for bug 1717040

I'll post my verification in steps, since the list of checks is long.

a) compression tests - xenial - PASS
ubuntu@xenial-zstd:~$ zstd /usr/bin/snap -o snap.0.5.1.zst
Compressed 17183248 bytes into 4541079 bytes ==> 26.43%
ubuntu@xenial-zstd:~$ ll snap.0.5.1.zst
-rw-rw-r-- 1 ubuntu ubuntu 4541079 Feb 19 17:52 snap.0.5.1.zst
ubuntu@xenial-zstd:~$

Package from proposed:
 *** 1.3.1+dfsg-1~ubuntu0.16.04.1 400
        400 http://br.archive.ubuntu.com/ubuntu xenial-proposed/universe amd64 Packages

ubuntu@xenial-zstd:~$ zstd /usr/bin/snap -o snap.1.3.1.zst
/usr/bin/snap : 24.91% (17183248 => 4281096 bytes, snap.1.3.1.zst)
ubuntu@xenial-zstd:~$ ll snap.1.3.1.zst
-rwxr-xr-x 1 ubuntu ubuntu 4281096 Nov 30 19:48 snap.1.3.1.zst*

Uncompressing:
ubuntu@xenial-zstd:~$ zstd -d snap.0.5.1.zst -o snap.0.5.1
snap.0.5.1.zst : 17183248 bytes
ubuntu@xenial-zstd:~$ zstd -d snap.1.3.1.zst -o snap.1.3.1
snap.1.3.1.zst : 17183248 bytes

md5 verification is OK:
ubuntu@xenial-zstd:~$ md5sum /usr/bin/snap snap.0.5.1 snap.1.3.1
50ff3c166c443c32f043294416a5b5d9 /usr/bin/snap
50ff3c166c443c32f043294416a5b5d9 snap.0.5.1
50ff3c166c443c32f043294416a5b5d9 snap.1.3.1

xenial downgrade fails to recognize the new format, as expected:
ubuntu@xenial-zstd:~$ zstd -d snap.1.3.1.zst -o /dev/null
zstd: /dev/null already exists; do you wish to overwrite (y/N) ? y
zstd: snap.1.3.1.zst: not in zstd format