Add unit tests for purge functionality

[TinaMor]

PR description

What does this PR do

Add unit tests for changes in PR #47

TODOs not included in this PR

1. Documentation of the purge flag

Relevant links ()

Follow up PR from PR #47

Checklist

As part of our commitment to engineering excellence, before submitting this PR, please make sure:

• You've tested this code in both Desktop & Server environments and AMD & ARM64 enviroments (functional testing).
• You've added unit tests for new code.
• You've added/updated documentation in the cmdlet docs, command-reference.md and the modules help files.
• You've reviewed the PR/code best practices defined in the CONTRIBUTING.md.

In addition, after this PR has been reviewed, please agree to:

• If changes have been made to your PR in the process of addressing comments, please make sure to test again the final version in both AMD and ARM64 environments.
• Validate your changes have not introduced any regressions.