Title: DiffTester: Accelerating Unit Test Generation for Diffusion LLMs via Repetitive Pattern
Primary area: foundation or frontier models, including LLMs
Keywords: diffusion LLM, unit test generation, inference acceleration, abstract syntax tree

Abstract: Software development relies heavily on extensive unit testing, which makes the efficiency of automated Unit Test Generation (UTG) particularly important. However, most existing LLMs generate test cases one token at a time in each forward pass, which leads to inefficient UTG. Recently, diffusion LLMs (dLLMs) have emerged, offering promising parallel generation capabilities and showing strong potential for efficient UTG. Despite this advantage, their application to UTG is still constrained by a clear trade-off between efficiency and test quality, since increasing the number of tokens generated in each step often causes a sharp decline in the quality of test cases. To overcome this limitation, we present **DiffTester**, an acceleration framework specifically tailored for dLLMs in UTG. The key idea of **DiffTester** is that unit tests targeting the same focal method often share repetitive structural patterns. By dynamically identifying these common patterns through abstract syntax tree analysis during generation, **DiffTester** adaptively increases the number of tokens produced at each step without compromising the quality of the output. To enable comprehensive evaluation, we extend the original TestEval benchmark, which was limited to Python, by introducing additional programming languages including Java and C++. Extensive experiments on three benchmarks with two representative models show that **DiffTester** delivers significant acceleration while preserving test coverage. Moreover, **DiffTester** generalizes well across different dLLMs and programming languages, providing a practical and scalable solution for efficient UTG in software development. Code and data are publicly available at https://anonymous.4open.science/r/DLM4UTG .

TL;DR: Acceleration of dLLM for Unit Test Generation via Repetitive Pattern