[Technical] xapi Statements test coverage

[DimitriB01]

Technical

Add tests to xapi related statements in the frontend.

Definition of Done

• [ ] All acceptance criteria are met
• [ ] The implementation of the User Story has been successfully accepted by the Product Owner
• [ ] The implementation is in GitHub
• [ ] A code review has been performed (or created in pairing program)
• [ ] Code conventions are followed
• [ ] Unit test coverage must be greater than 90%
• [ ] All tests must have passed
• [ ] Technical documentation created (Feature documented in GitHub Wiki)
• [ ] UML class diagrams and component diagrams created and up-to-date
• [ ] Documentation in realization created (source code)
• [ ] Changelog created (Clear description in merge request)
• [ ] There are no known bugs
• [ ] Rendering behaviour is optimized