Testing Method Relocation Algorithms via Template-Based Systematic Structural Traversal and Precondition Filtering

Method relocation refactorings, primarily Move Method and Pull Up/Push Down Method, are indispensable for reducing coupling and enhancing cohesion. Despite their widespread automation in modern refactoring engines, these algorithms remain notoriously error-prone, posing significant risks to software reliability. A primary challenge in testing them lies in the vast search space of complex program structures and the intricate preconditions required for safe method relocation. To address this, we propose RelocTest, a comprehensive testing framework that combines template-driven structural traversal with automated precondition filtering. RelocTest systematically explores the input space by populating program templates specially designed for method relocation through a two-stage generation process: (1) Skeleton Synthesis, which systematically traverses diverse syntactic structures, and (2) LLM-Guided Completion, which leverages Large Language Models to inject diverse, executable code into these skeletons. This hybrid strategy ensures high structural coverage while maintaining test program validity. Furthermore, to optimize testing efficiency, we introduce an LLM-based Precondition Extractor that analyzes the implementation of method relocation algorithms to identify and prune test programs destined for rejection. We evaluated RelocTest on 7 mainstream refactoring engines. Our approach successfully uncovered 56 previously unknown bugs, with 19 already confirmed by tool vendors, demonstrating its effectiveness in hardening industrial-strength refactoring tools.