FOI: bats-assert

[yarikoptic]

https://github.com/ztombol/bats-assert provides a nice collection of assertion helpers to be used in bats, similar to the ad-hoc ones I started to introduce in #27 . Would be nice to migrate those to use the ones from bats-assert

TODO to the Debian maintainer of bats -- package bats-assert as well ;-)

[mjtravers]

Ah, nice find.

assert_output --partial 'arg #1='

is much easier to remember and read than:

[ "${lines[0]}" = 'arg #1=' ]