ACES: Who Tests the Tests? Leave-One-Out AUC Consistency for Code Generation

2026-04-04

AI Summary

This work addresses the challenge that existing large language model–based methods for generating test cases often produce potentially flawed tests, making test quality difficult to assess and creating a circular dependency between test validity and code correctness. To resolve this, the authors propose the ACES scoring framework, which reframes test evaluation as a ranking consistency problem. ACES introduces leave-one-out AUC (LOO-AUC) to measure a test’s ability to discriminate between correct and incorrect code without requiring absolute judgments of test correctness. Operating on a binary pass-fail matrix, ACES enables efficient weighted ranking via either closed-form weight computation or differentiable optimization, yielding two scalable variants: ACES-C and ACES-O. Experiments demonstrate that ACES significantly improves Pass@$k$ performance across multiple code generation benchmarks, achieving state-of-the-art results with minimal computational overhead.

Abstract

Selecting LLM-generated code candidates using LLM-generated tests is challenging because the tests themselves may be incorrect. Existing methods either treat all tests equally or rely on ad-hoc heuristics to filter unreliable tests. Yet determining test correctness requires knowing which codes are correct, creating a \emph{circular dependency}. Our key insight is that we need not determine test correctness at all: \emph{test votes should rank, not merely count}. What matters is not how many codes pass a test, but whether the test can \emph{distinguish} correct from incorrect code. We break the circular dependency via leave-one-out evaluation: hold out one test, rank codes by their aggregate scores on all remaining tests, and measure whether the held-out test's pass/fail pattern agrees with this ranking. We formalize this agreement as the leave-one-out AUC~(LOO-AUC) and prove that the expected LOO-AUC is proportional to each test's ability to separate correct code from incorrect code. Building on this, we propose \textbf{ACES}~(\textbf{A}UC \textbf{C}onsist\textbf{E}ncy \textbf{S}coring) with two complementary variants: ACES-C provides closed-form weights that provably approximate the oracle in expectation under a mild assumption on average test quality; ACES-O drops this assumption and iteratively optimizes a differentiable LOO-AUC objective. Both operate solely on the binary pass matrix with negligible overhead, and achieve state-of-the-art Pass@$k$ on multiple code generation benchmarks.

Problem

• code generation
• test reliability
• circular dependency
• LLM-generated tests
• code evaluation

Innovation

• LOO-AUC
• test weighting
• code generation
• circular dependency
• ACES