I've been successfully integrating the Foundation Models framework into my healthcare app using structured generation with @Generable schemas. While my initial testing (20-30 iterations) shows promising results, I need to validate consistency and reliability at scale before production deployment.
Question
Is there a recommended approach for automated, large-scale testing of Foundation Models responses? Specifically, I'm looking to:
- Automate 1000+ test iterations with consistent prompts and structured schemas
- Measure response consistency across identical inputs
- Validate structured output reliability (proper schema adherence, no generation failures)
- Collect performance metrics (TTFT, TPS) for optimization
Specific Questions
- Framework Limitations: Are there any undocumented rate limits or thermal throttling considerations for rapid session creation/destruction?
- Performance Tools: Can Xcode's Foundation Models Instrument be used programmatically, or only through Instruments UI?
- Automation Integration: Any recommendations for integrating with testing frameworks?
- Session Reuse: Is it better to reuse a single LanguageModelSession or create fresh sessions for each test iteration?
Use Case Context
My wellness app provides medically safe activity recommendations based on user health profiles. The Foundation Models framework processes health context and generates structured recommendations for exercises, nutrition, and lifestyle activities. Given the safety implications of providing health-related guidance, I need rigorous validation to ensure the model consistently produces appropriate, well-formed recommendations across diverse user scenarios and health conditions.
Has anyone in the community built similar large-scale testing infrastructure for Foundation Models? Any insights on best practices or potential pitfalls would be greatly appreciated.
Let me start with my own answer. Folks are welcome to jump in with more comments.
- Automate 1000+ test iterations with consistent prompts and structured schemas
To fully control the evaluation process, I use my own tool to automatically load a data set, run through it, and gather the responses. I guess you can do so as well. Writing test cases should also work.
- Measure response consistency across identical inputs
- Validate structured output reliability (proper schema adherence, no generation failures)
Measuring response consistency is an important topic, and you will need to do it with your own way. For example, you can use other models to vectorize the responses and do semantic similarity comparison; you can even ask a frontier model to score the similarity of two response.
For a response defined with a Generable type, you can use your code to convert the type to a string representation, and then do the comparison. This will also help the validation of the structured output.
- Collect performance metrics (TTFT, TPS) for optimization
If you have code to receive a stream response, you can calculate the responding time from there.
- Framework Limitations: Are there any undocumented rate limits or thermal throttling considerations for rapid session creation/destruction?
Rate limiting applies when you device is on battery AND when your process is running in the background, and so you'd be able to avoid that by running your tests on a device connecting to power.
- Performance Tools: Can Xcode's Foundation Models Instrument be used programmatically, or only through Instruments UI?
You can run the command line xcrun xctrace record --template "Foundation Models"... to record a trace. You will need to analyze the trace with Instruments.app however.
- Automation Integration: Any recommendations for integrating with testing frameworks?
I am unclear what testing framework you are using... I don't see anything preventing you from using Swift Testing to test the use of Foundation Models though. I'll be super curious if you see any issue in this area.
- Session Reuse: Is it better to reuse a single LanguageModelSession or create fresh sessions for each test iteration?
Prompts to a same session shares the session configuration (the instructions, tools, and options) and the context (the dialog that has happened, and the context size). Unless you'd intentionally test a series of prompts with the same configuration, you'd probably use a new session for every test.
Best,
——
Ziqiao Chen
Worldwide Developer Relations.