A method to identify overfitting program repair patches based on expression tree

The primary aim of Automatic Program Repair (APR) is to automatically repair defective programs, with the intention of reducing the amount of effort required by developers. However, APR techniques may produce overfitting patches that do not truly repair the program, allowing the program to pass all test cases. This paper provides a comprehensive review of the overfitting problem and adds to the existing research on overfitting in conditional statements. Our proposed method, ETPAT (Expression Tree-based Patch Assessment Technique), implements expression trees and targeted coverage criteria to identify differences between the original and the patched program. We utilize ETPAT to verify test case adequacy. In parallel, ETPAT also guides the generation of corresponding test cases via equivalence class information, which may be added to the original test suite, making it more robust while also preventing the repair technique from generating comparable overfitting patches. With reference to the patch set in the BuggyJavaJML benchmark, ETPAT recognized 77/82 (93.9%) overfitting patches out of 120 patches related to conditional constraints, displaying superior accuracy rates and fewer test cases required than the original repair tool.