Curate the Design (TDD with SwiftUI)

With TDD, it's really important to stay on top of continually curating the design. This means paying attention to code smells and design anti-patterns, like the Law of Demeter.

[QualityCoding]

Retro notes:
- "Move Field" of @State requires more changes
- Law of Demeter
- Tell, don't ask
- Guess still needs to be Observable
- No need to add tests for extracted methods