The “Question Neighbourhood” Approach for Systematic Evaluation of Code-Generating LLMs

We present the concept of a question neighbourhood for systematically evaluating instruction-tuned large language models (LLMs) for code generation via a new benchmark, Turbulence. Turbulence consists of a large set of natural language question templates, each of which is a programming problem, parameterised so that it can be asked in many different forms. Each question template has an associated test oracle that judges whether a code solution returned by an LLM is correct. Thus, from a single question template, it is possible to ask an LLM a neighbourhood of very similar programming questions, and assess the correctness of the result returned for each question. This allows gaps in an LLM’s code generation abilities to be identified, including anomalies where the LLM correctly solves many questions in a neighbourhood but fails for particular parameter instantiations. We present experiments against 22 state-of-the-art proprietary and open-source LLMs, each at two temperature configurations. Our evaluation is based on three complementary scores: accuracy score, correctness-potential score, and consistent-correctness score. Our findings show that, across the board, Turbulence is able to reveal cases where LLMs do not behave in a correct and consistent manner, highlighting gaps in their reasoning ability. This goes beyond merely highlighting that LLMs sometimes produce wrong code (which is no surprise): by systematically identifying cases where LLMs are able to solve some problems in a neighbourhood but do not manage to generalise to solve the whole neighbourhood, our method provides detailed insight into the behavioural characteristics of current code-generating LLMs. We present data and examples that shed light on the kinds of mistakes that LLMs make when they return incorrect code results.