Unit tests for JS Pack component
Summary: Unit tests.
Test Plan: Irrelevant.
Reviewers: O2 JS Simulation, Itms, wraitii
Reviewed By: O2 JS Simulation, wraitii
Subscribers: O8 JS GUI, O14 Maps, O6 AI, Sandarac, Vulcan
Differential Revision: https://code.wildfiregames.com/D240