Integration tests

[AntoMars14]

This pull request introduces a minimal, robust integration testing setup for the backend, focusing on HTTP-level API and database persistence tests. It establishes clear guidelines for integration test scope and structure, adds foundational test infrastructure, and migrates existing tests to NUnit for consistency and maintainability.

Integration test infrastructure and guidelines:

• .github/agents/backend-integrationtests-agent.md: Added a comprehensive agent profile and requirements document, specifying integration test scope, placement, standards, and determinism rules for backend API and database testing.

API integration tests:

• ServerTests/Integration/Api/BasicReachabilityTests.cs: Introduced a basic HTTP-level API integration test using NamTestFactory and NUnit to verify the /health endpoint is reachable and returns 200 OK.
• ServerTests/Integration/Shared/NamTestFactory.cs: Added a custom WebApplicationFactory implementation for test server setup, using SQLite in-memory database and test authentication, to support stable, isolated API integration tests.
• ServerTests/Integration/Shared/TestAuthHandler.cs: Implemented a test authentication handler to enable fake user authentication in integration tests.

Database integration tests:

• ServerTests/Integration/Database/PersistenceTests.cs: Added database integration tests using SQLite in-memory, verifying persistence and retrieval of various entities (User, MapMarker, MapData, MunicipalityCard) across contexts.

Test framework consistency:

• ServerTests/NamServer/Endpoints/Auth/AuthLoginTests.cs, ServerTests/NamServer/Endpoints/Auth/RegistrationTests.cs: Migrated existing MSTest-based tests to NUnit, updating attributes and assertions for consistency; removed MSTest parallelization settings. [1] [2] [3] [4] [5]

These changes lay the foundation for reliable backend integration testing, ensuring coverage at the HTTP boundary and database layer, and enforcing consistent test standards across the codebase.