Writing llmock Test Fixtures

What llmock Is

Zero-dependency mock LLM server. Fixture-driven. Multi-provider (OpenAI, Anthropic, Gemini, AWS Bedrock, Azure OpenAI). Runs a real HTTP server on a real port — works across processes, unlike MSW-style interceptors. WebSocket support for OpenAI Responses/Realtime and Gemini Live APIs.

Core Mental Model

• Fixtures = match criteria + response
• First-match-wins — order matters
• All providers share one fixture pool (provider adapters normalize to ChatCompletionRequest)
• Fixtures are live — mutations after start() take effect immediately
• Sequential responses are supported via sequenceIndex (match count tracked per fixture)

Match Field Reference