How I test AI agent frontends without calling the...

How I test AI agent frontends without calling the API once Testing AI agent applications is broken. Not the model calls — those you can mock. What nobody knows how to test is the streaming layer: the event sequence your frontend actually receives, the state transitions that happen across a multi-turn agent loop, the subtle timing between a tool_use and its tool_result. Most teams either skip this entirely or write flaky integration tests that hit the real API on every CI run. There's a better wa