Testing AI Agent Frontends Without the API: Stream Recording as a Test Fixture

Testing AI agent applications traditionally requires either calling the real API (slow and non-deterministic) or mocking event sequences (brittle and unrealistic). This approach captures production streaming events as JSONL fixtures, enabling deterministic replay of real event sequences—including timing and state transitions—without API calls. By treating production streams as regression test suites, teams can automatically build robust tests for complex streaming behaviors that are typically skipped or tested only through flaky integration tests.