LLM function-calling tests should focus on schema compliance, not model behavior

This article discusses the importance of contract testing for function-calling schema compliance in LLMs. It differentiates between testing model behavior (e.g., whether it calls a specific tool) and testing contract compliance (e.g., whether the tool call adheres to the defined schema). The author advocates for deterministic tests that assert the structure and validity of tool calls, rather than their specific arguments or whether the model chose a particular function. Key assertions include checking the `finish_reason`, the presence and type of `tool_calls`, and ensuring the `function.name` is within the declared set. Crucially, it highlights that `function.arguments` should be a JSON-encoded string, not a parsed object, to avoid compatibility issues with downstream parsers. AI

IMPACT Provides guidance for developers integrating LLMs, improving reliability of tool-use.

RANK_REASON Article provides technical advice and best practices for testing LLM function calls, not a new release or significant industry event.

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