Implement Updater Integration Tests

[deeplow]

• [x] I have searched for duplicates or related issues

Description

The current updater does have unit tests. However, it is lacking integration tests and we are currently relying on manual validation for that part. We should have these integrations tests in order to catch:

• Qubes updater bugs
• Bugs in how we interface with the Qubes Updater. Examples we manually caught:
  • https://github.com/freedomofpress/securedrop-workstation/issues/1127
  • https://github.com/freedomofpress/securedrop-workstation/issues/1140

How will this impact SecureDrop/SecureDrop Workstation users?

Dev-facing / no impact.

How would this affect the SecureDrop Workstation threat model?

Dev-facing / no impact.

User Stories

As a developer, I don't want to rely on manual testing.

[deeplow]

Implementation ideas

Setup:

• install a package (e.g. htop) on dom0 and all sdw-managed templates
• then downgrade said package (e.g. qubes-dom0-update --action=downgrade htop)

When:

• SDW Updater is run

Then:

• Qubes events detect correct template startups and app qube restarts / shutdowns
• qvm-prefs tags for last-updated are correctly updated