add a test for get_pdu and initialize_from_db

Add a test for get_pdu_from_db and initialize_from_db

Description

How Has This Been Tested?

Relevant Documents (optional)

Types of changes

• Adding tests

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.

Reviewers

@roscar @danilevc @hammerd