# Testing and Code Quality Rules

- **No non-null assertions**: Non-null assertions (the `!` operator) are a hack for missing null checks or extraneous null types. Always use proper null checks and handle possible null/undefined values explicitly.
- **Do not throw errors within tests**: Use proper test assertions (e.g., `expect(value).not.toBeNull()`) instead of throwing errors from within tests. This ensures test failures are reported clearly and consistently.
- **Do not use `any`**: Use proper types instead of `any`.
- **Do not use `jest.fn()`**: Use proper test assertions (e.g., `expect(value).not.toBeNull()`) instead of throwing errors from within tests. This ensures test failures are reported clearly and consistently.
- **Use the in-memory database for tests**: Use the in-memory database for tests. This is a good way to test the code without having to set up a real database.
- **Always use repositories for database operations**: Use repositories for database operations. This is a good way to test the code without having to set up a real database.