Chore: Add unit tests for string functions

[madsrasmussen]

Description

Adds unit tests for string functions

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Chore (minor updates related to the tooling or maintenance of the repository, does not impact compiled assets)