arXiv subjects

Kosei Horikawa

Publications and source records attributed to Kosei Horikawa.

6 recordsLinked to original sources

arXiv2026

Is Self-Admitted Technical Debt Tested? An Empirical Study of Coverage, Co-change, and Impact

When developers write a TODO or FIXME comment, they are explicitly admitting that the code is suboptimal: a built-in warning that this logic deserves extra scrutiny. Yet it is an open question whether Self-Admitted Technical Debt (SATD) actually receives that scrutiny in the form of software testing. We aim to characterize the relationship between SATD and testing across three dimensions: the extent to which SATD-affected code is covered by existing tests, whether developers synchronize test additions with debt resolution, and whether such testing affects the long-term observability of resulting defects. For that, we conducted an empirical study on eight open-source Java projects, analyzing test coverage of 784 SATD instances identified in the latest releases and performing a longitudinal examination of 5,175 SATD removal events. Our results show that while 60.7% of SATD-affected code is covered by existing test suites, developers rarely synchronize test modifications with debt resolution; manual inspection confirms that only 3.4% of SATD removal commits include new tests specifically targeting the resolved debt (vs. 12.5% that co-add tests in the same commit). Longitudinal analysis further suggests that SATD resolutions exhibit nearly identical localized bug induction rates within short-to-medium-term windows regardless of test modifications. However, over a longer, unrestricted observation window, a slight divergence emerges where the test-added group reaches a higher cumulative defect alignment probability (6.32% vs. 4.37%), a counterintuitive trend potentially driven by the selective testing of inherently complex components. Developers treat SATD repayment as an ordinary code change rather than as a high-risk maintenance activity: most debt removals proceed without targeted verification, despite the developer's own prior flag that the code is suboptimal.

cs.SE↗

arXiv2026

AgentLogs: A Dataset for Opening the Black Box of GitHub's Cloud Agent

Generative AI-based software engineering agents are becoming routine contributors to real-world software projects. On GitHub, developers can assign tasks to the Copilot cloud agent, which autonomously explores the repository, edits code, runs commands, and opens or reviews pull requests, producing a detailed log of every step along the way. While existing datasets capture outcomes of agent contributions, such as agent-authored pull requests, the process by which agents produce these contributions remains largely unexplored. To address this gap, we introduce AgentLogs, a large-scale dataset of agent activity on GitHub. AgentLogs comprises 307,416 agent tasks and 549,239 agent sessions in 35,810 of the 1,812,362 popular public repositories that we scanned, together with 64,255,174 session log entries that record each agent run step by step, including prompts, intermediate reasoning, tool calls (e.g., file edits, git operations, and GitHub interactions), and token usage. By exposing not only what agents contribute but also how they work, AgentLogs enables research on agent behavior, efficiency and cost, task formulation, failure modes, and human-agent collaboration in agentic software engineering.

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arXiv2026

What Are Developers Actually Discussing When Visual Regression Tests Fail?

Visual Regression Tests (VRTs) are widely adopted as a mechanism for detecting unintended visual changes in user interfaces. By design, VRTs operate on rendered pixel output, and the prevailing assumption is that they catch stylistic regressions such as layout shifts, color mismatches, and font alterations. We conduct an empirical analysis of 307 pull requests (PRs) from 103 GitHub repositories that incorporate VRT results via Chromatic, comparing them against 299 PRs that contain image attachments but no VRT (Visual PRs). Quantitatively, VRT-PRs show no significant acceptance-rate difference, but exhibit a 3.8 times longer median resolution time, 10 times more discussion comments, and 1.75 to 4.5 times larger code changes than Visual PRs. VRT results are typically shared around the midpoint of the review process, sustaining ongoing discussion rather than serving only as a final check. Through a card-sorting analysis of 189 VRT-flagged issues, we identify seven defect categories assigned to the analyzed issues: Layout (39.7\%), Appearance (27.5\%), Color (14.8\%), Text (9.5\%), State (6.9\%), Test (6.3\%), and Image (4.2\%). The three most frequent categories are stylistic, while approximately 18.5\% of analyzed issues (35/189) involve non-stylistic origins, including undefined component state (13 cases), content disappearance (17 cases across multiple categories), and visually imperceptible regressions (5 cases). We further document cases in which VRT detected visual regressions originating from code changes in seemingly unrelated files, exposing non-local effects that no targeted test would have been written to catch. These observations indicate that, in addition to its primary role as a stylistic checker, VRT functions as a secondary detector of unintended consequences of code changes, with implications for how VRT should be integrated into the maintenance toolchain.

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arXiv2026

Do AI Agents Really Improve Code Readability?

Code readability is fundamental to software quality and maintainability. Poor readability extends development time, increases bug-inducing risks, and contributes to technical debt. With the rapid advancement of Large Language Models, AI agent-based approaches have emerged as a promising paradigm for automated refactoring, capable of decomposing complex tasks through autonomous planning and execution. While prior studies have examined refactoring by AI agents, these analyses cover all forms of refactoring, including performance optimization and structural improvement. As a result, the extent to which AI agent-based refactoring specifically improves code readability remains unclear. This study investigates the impact of AI agent-based refactoring on code readability. We extracted commits containing readability-related keywords from the AIDev dataset and analyzed changes in readability metrics before and after each commit, covering 403 commits evaluated using multiple quantitative metrics. Our results indicate that AI agents primarily target logic complexity (42.4%) and documentation improvements (24.2%) rather than surface-level aspects like naming conventions or formatting. However, contrary to expectations, readability-focused commits often degraded traditional quality metrics: the Maintainability Index decreased in 56.1% of commits, while Cyclomatic Complexity increased in 42.7%.

cs.SE↗

arXiv2026

Testing with AI Agents: An Empirical Study of Test Generation Frequency, Quality, and Coverage

Agent-based coding tools have transformed software development practices. Unlike prompt-based approaches that require developers to manually integrate generated code, these agent-based tools autonomously interact with repositories to create, modify, and execute code, including test generation. While many developers have adopted agent-based coding tools, little is known about how these tools generate tests in real-world development scenarios or how AI-generated tests compare to human-written ones. This study presents an empirical analysis of test generation by agent-based coding tools using the AIDev dataset. We extracted 2,232 commits containing test-related changes and investigated three aspects: the frequency of test additions, the structural characteristics of the generated tests, and their impact on code coverage. Our findings reveal that (i) AI authored 16.4% of all commits adding tests in real-world repositories, (ii) AI-generated test methods exhibit distinct structural patterns, featuring longer code and a higher density of assertions while maintaining lower cyclomatic complexity through linear logic, and (iii) AI-generated tests contribute to code coverage comparable to human-written tests, frequently achieving positive coverage gains across several projects.

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arXiv2025

Agentic Refactoring: An Empirical Study of AI Coding Agents

Agentic coding tools, such as OpenAI Codex, Claude Code, and Cursor, are transforming the software engineering landscape. These AI-powered systems function as autonomous teammates capable of planning and executing complex development tasks. Agents have become active participants in refactoring, a cornerstone of sustainable software development aimed at improving internal code quality without altering observable behavior. Despite their increasing adoption, there is a critical lack of empirical understanding regarding how agentic refactoring is utilized in practice, how it compares to human-driven refactoring, and what impact it has on code quality. To address this empirical gap, we present a large-scale study of AI agent-generated refactorings in real-world open-source Java projects, analyzing 15,451 refactoring instances across 12,256 pull requests and 14,988 commits derived from the AIDev dataset. Our empirical analysis shows that refactoring is a common and intentional activity in this development paradigm, with agents explicitly targeting refactoring in 26.1% of commits. Analysis of refactoring types reveals that agentic efforts are dominated by low-level, consistency-oriented edits, such as Change Variable Type (11.8%), Rename Parameter (10.4%), and Rename Variable (8.5%), reflecting a preference for localized improvements over the high-level design changes common in human refactoring. Additionally, the motivations behind agentic refactoring focus overwhelmingly on internal quality concerns, with maintainability (52.5%) and readability (28.1%). Furthermore, quantitative evaluation of code quality metrics shows that agentic refactoring yields small but statistically significant improvements in structural metrics, particularly for medium-level changes, reducing class size and complexity (e.g., Class LOC median $Δ$ = -15.25).

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