Fix an issue where proxied data was not being re-assigned, stabilize observer map test

[janechu]

Pull Request

📖 Description

This change ensures that the internal test element in observer map fixture is defined first, then the wrapping test element. It also ensures that proxied data is being re-assigned instead of the original data structure.

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.