Split the sources and the tests

[pBouillon]

Issue Summary

The sources and their test files are mixed up together.

Many libraries have a separate src/ and spec/ folders to avoid this concern.

Category

- [ ] Bug report
- [ ] Regression
- [ ] Feature suggestion
- [ ] Documentation issue
- [x] Other

Expected Behavior

Create a spec/ folder and move the tests into it.

All tests should still be executed when using ng test or when the CI is run.

Actual Behavior

Currently, the specs and the sources are all in the src folder.

Steps to Reproduce

N/A

Environment

• Browser/Device: N/A
• Node version: N/A
• Version: N/A

Additional Information

N/A