Fixing mypy issues in tests

tests/test_heartbeat.py

@@ -1,20 +1,24 @@
+from typing import Any, Generator
+
+from flask.testing import FlaskClient
 import pytest
+
 from src.app import app
 
 
 @pytest.fixture
-def client():
+def client() -> Generator[FlaskClient, Any, Any]:
     app.config["TESTING"] = True
     with app.test_client() as client:
         yield client
 
 
-def test_heartbeat_status_code(client):
+def test_heartbeat_status_code(client: FlaskClient) -> None:
     response = client.get("/heartbeat")
     assert response.status_code == 200
 
 
-def test_heartbeat_payload(client):
+def test_heartbeat_payload(client: FlaskClient) -> None:
     response = client.get("/heartbeat")
     data = response.get_json()
     assert data["status"] == "ok"