[Test] Modernize the tests for the Zen Mode ability

[DayKev]

What are the changes the user will see?

N/A

Why am I making these changes?

The test file is very outdated/questionable.

What are the changes from a developer perspective?

The Zen Mode tests are more comprehensible (and more accurate?).

How to test the changes?

npm run test zen_mode

Checklist

• I'm using beta as my base branch
• There is no overlap with another PR?
• The PR is self-contained and cannot be split into smaller PRs?
• Have I provided a clear explanation of the changes?
• Have I considered writing automated tests for the issue?
• [ ] If I have text, did I make it translatable and add a key in the English locale file(s)?
• [ ] Have I tested the changes (manually)?
  • Are all unit tests still passing? (npm run test)
• [ ] Are the changes visual?
  • [ ] Have I provided screenshots/videos of the changes?