Add tests for Event model and new mock_user fixture

Introduce comprehensive tests for the Event model, covering creation, updates, deletions, relationships, defaults, and constraints. Added the `mock_user` fixture to streamline user-related test setups and ensure proper linkage between users and events. Improves test coverage and ensures model behavior consistency.

backend/tests/conftest.py

@@ -1,9 +1,10 @@
 # tests/conftest.py
 import pytest
-from sqlalchemy.orm import Session, sessionmaker
-
+import uuid
+from app.models.user import User
 from app.utils.test_utils import setup_test_db, teardown_test_db
 
+
 @pytest.fixture(scope="function")
 def db_session():
     """
@@ -19,4 +20,22 @@ def db_session():
         yield session
 
     # Clean up
-    teardown_test_db(test_engine)
+    teardown_test_db(test_engine)
+
+
+@pytest.fixture
+def mock_user(db_session):
+    """Fixture to create and return a mock User instance."""
+    mock_user = User(
+        id=uuid.uuid4(),
+        email="mockuser@example.com",
+        password_hash="mockhashedpassword",
+        first_name="Mock",
+        last_name="User",
+        phone_number="1234567890",
+        is_active=True,
+        is_superuser=False
+    )
+    db_session.add(mock_user)
+    db_session.commit()
+    return mock_user