## Description Add backend tests for authentication and gallery creation flows. ## Done when - [x] User registration is tested. - [x] Duplicate usernames are rejected. - [x] Login works with valid credentials. - [x] Login fails with invalid credentials. - [x] Creating a gallery is tested. - [x] Adding an artwork to a gallery is tested. - [x] Users cannot modify another user's gallery. - [x] Adding the same artwork multiple times is handled correctly.