Comment 6 for bug 1595813

Verification done with a snap created from this snapcraft.yaml file:

name: test-snapd-upower-observe-consumer
version: 1.0
summary: Basic upower-observe consumer snap
description: A basic snap declaring a plug on upower-observe

apps:
    upower:
        command: upower
        plugs: [upower-observe]

parts:
    upower:
        plugin: nil
        stage-packages: [upower]

After installing this is the interfaces list:

fgimenez@innsmouth:~/Downloads/upower-snap$ snap interfaces
Slot Plug
[...]
:upower-observe test-snapd-upower-observe-consumer
[...]

And the upower binary wrapped by the snap works as expected:

fgimenez@innsmouth:~/Downloads/upower-snap$ test-snapd-upower-observe-consumer.upower
fgimenez@innsmouth:~/Downloads/upower-snap$ test-snapd-upower-observe-consumer.upower --help
Usage:
  upower [OPTION...] UPower tool

Help Options:
  -h, --help Show help options

Application Options:
  -e, --enumerate Enumerate objects paths for devices
  -d, --dump Dump all parameters for all objects
  -w, --wakeups Get the wakeup data
  -m, --monitor Monitor activity from the power daemon
  --monitor-detail Monitor with detail
  -i, --show-info Show information about object path
  -v, --version Print version of client and daemon

fgimenez@innsmouth:~/Downloads/upower-snap$ test-snapd-upower-observe-consumer.upower -e
/org/freedesktop/UPower/devices/line_power_ADP1
/org/freedesktop/UPower/devices/battery_BAT1
/org/freedesktop/UPower/devices/DisplayDevice