test: add assert statements in hello_world agent main.py

They will check the states of the agent after each die roll.

PiperOrigin-RevId: 769949096

Author: wuliang229

contributing/samples/hello_world/main.py

@@ -70,12 +70,22 @@ async def run_prompt_bytes(session: Session, new_message: str):
       if event.content.parts and event.content.parts[0].text:
         print(f'** {event.author}: {event.content.parts[0].text}')
 
+  async def check_rolls_in_state(rolls_size: int):
+    session = await runner.session_service.get_session(
+        app_name=app_name, user_id=user_id_1, session_id=session_11.id
+    )
+    assert len(session.state['rolls']) == rolls_size
+    for roll in session.state['rolls']:
+      assert roll > 0 and roll <= 100
+
   start_time = time.time()
   print('Start time:', start_time)
   print('------------------------------------')
   await run_prompt(session_11, 'Hi')
   await run_prompt(session_11, 'Roll a die with 100 sides')
+  await check_rolls_in_state(1)
   await run_prompt(session_11, 'Roll a die again with 100 sides.')
+  await check_rolls_in_state(2)
   await run_prompt(session_11, 'What numbers did I got?')
   await run_prompt_bytes(session_11, 'Hi bytes')
   print(