[Feature] Tests for onPostBuild

# **Feature Request**

## **Is your feature request related to a problem? Please describe.**

Currently no tests exist for onPostBuild. This hook is where changes are made in the HTML source including replacing URLs with Cloudinary URLs.

## **Describe the solution you'd like**

Test cases should include but not limited to:
- Delivery Type: fetch vs upload
- Images Path: 1 vs multiple