EPIC: TDD for backend

[romaneriksen]

What
Implement a comprehensive test framework for the backend, using test-driven development (TDD) principles. This should cover core functionality, including class methods, service functions, and API endpoints.

Why

• Ensure backend functionality works as expected and meets specifications.
• Minimize integration issues when connecting with the frontend.
• Enable safer refactoring and long-term maintainability.
• Provide clear examples and templates for writing future tests.

How

• Follow the Arrange-Act-Assert (AAA) pattern in all tests.
• Create unit tests for core functions and integration tests for endpoints.
• Use NUnit and maintain consistent test structure.
• Document test setup and expected outcomes so other developers can extend tests easily.

Acceptance Criteria

• Core backend functionality has at least (some percentage)% test coverage. ??
• All existing endpoints and critical business logic are covered with passing tests.
• Tests are structured clearly, following AAA, and include descriptive naming for readability.
• Documentation exists for adding new tests.