Test framework issues when updating agent from tool

[Kedaqusa1604]

Bug Description

Hi, I'm trying to test a multi-agent application but I'm facing issues when trying to test it following this guide:

https://docs.livekit.io/agents/start/testing/test-framework/#overview

The app starts at "Agent 1" which uses a tool that updates the session agent inside it in the following way:

#Agent 1

@function_tool
async def tool(ctx: RunContext):
     await ctx.update("")
     forward_agent = Agent2()
     async with ctx.foreground():
        session = ctx.session
        session.update_agent(forward_agent)
     
     return None

class Agent2(Agent):
   async def on_enter(self):
      await self.session.generate_reply("Tell a joke")

and the test script is something like this:

#test_script.py 

result.expect.next_event().is_function_call(
    name = "tool",
    arguments = ...
)

result.expect.next_event().is_function_call_output(
    output = ""
)

await result.expect.next_event().is_message(role = "assistant").judge(
    llm,
    intent = ...
)

But when I run the test script, I'm getting the following error:

Debugging the test, I noticed that the tool invocation only emits these two events:

FunctionCallEvent
FunctionCallOutputEvent

The MessageEvent generated by Agent2 never reaches the test framework, even though the application behaves correctly outside the testing environment.

In production, after session.update_agent(forward_agent) is called, Agent2.on_enter() is executed, generate_reply() is called, and the assistant responds as expected.

My questions are:

• Is there a supported way to continue listening for events emitted by the new agent after update_agent()?0
• Or is there a different recommended way to test multi-agent handoffs where the second agent immediately generates a reply?

Any guidance would be greatly appreciated.

Expected Behavior

Reproduction Steps

1. 
2.
3.
...
- Sample code snippet, or a GitHub Gist link -

Operating System

Linux

Models Used

Gemini-3.5-flash-lire

Package Versions

livekit==1.1.13
livekit-agents==1.6.5
livekit-api<2

Session/Room/Call IDs

No response

Proposed Solution

Additional Context

No response

Screenshots and Recordings

No response