Add module tests to catch breaking changes

Several kinds of tests may be useful here:
* Unit tests for the Engine project to ensure objects are created and passed around as expected
* E2E tests inside a function app using the same project structure as worker and the Durable SDK
* Pester testing the module outside the context of Functions (?)

Start by locating the Engine project and the function app structure used by the worker and Durable SDK. Compare the proposed unit, end-to-end, and Pester approaches, then define which module behaviors must be covered so tests reliably catch breaking changes.

Written by the indexing model from the issue text.