test: improve readability via hash item helper fn (agama-project#1732)

## Problem

As I was reviewing agama-project#1716 I noticed it was touching some repetitive code
to set up test data

## Solution

Don't bury the actual test data among so much boilerplate.
Diff: +85 -236


## Testing

`cargo test` continues to work ✔️ 

## Screenshots

N/A