Add Unit Tests for Library Features

Let's boost our library's reliability! We need unit tests for each feature.

**Features to be Tested:**

- [ ] Rerender Element with Watch
- [ ] Create Getter/Setters with getset
- [ ] Create Property Reflection with propReflect
- [ ] Create Inline Events with event
- [ ] Create Custom Events with emit
- [ ] Inject Global Styles with injectStyles
- [ ] Other features...

**How You Can Help:**

1. Pick a feature.
2. Write clear test cases.
3. Cover edge cases.
4. Follow naming conventions.
5. Submit a pull request!

**Ready to Contribute?**

1. Comment to claim a feature.
2. Fork the repo.
3. Create a new branch.
4. Submit a pull request!

Let's make testing our library fun and collaborative! 🚀

Start by locating the implementations and test setup for Watch, getset, propReflect, event, emit, and injectStyles. Add unit tests covering the listed features and relevant edge cases, following the repository's naming conventions; done means each named feature has clear test coverage.

Written by the indexing model from the issue text.