Verification Trap: Understanding Test-Time Selection Failures under False Premises in Code Generation

Feng He, Hejia Wang, Linghao Meng, Ming Gao, Qiankun Li


Abstract
Test-time compute has become a central way to improve code generation: systems sample multiple candidate programs and use verifier-visible evidence to select the final output. This paradigm implicitly assumes that the verifier provides a corrective signal independent from the generator. We challenge this assumption under misleading task premises. When the generator and verifier share a false premise, they become coupled through a mistaken belief: the generator produces premise-consistent shortcuts, while the verifier supplies evidence that fails to expose them. Consequently, the selector may choose a hidden-test-wrong candidate even when a hidden-test-correct program exists in the pool. We call this failure mode Verification Trap. Across three code-generation benchmarks and five code models, false premises consistently degrade first-sample correctness, reduce selector-chosen correctness after 64-sample test-time selection, and amplify recoverable mis-selection. Mechanistically, verifier-written tests inherit the premise-level blind spot, reshaping verifier-visible candidate space away from hidden-test correctness. These traces make Verification Trap predictable before hidden execution: a lightweight gold-free predictor using verifier-visible features reaches 0.846 AUROC. Our results identify decoupled evidence as a key mitigation axis: coupled scaling provides limited recovery, whereas premise-agnostic robustness auditors recover substantial oracle headroom.
Anthology ID:
2026.emnlp-main.157
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
3613–3637
Language:
URL:
https://aclanthology.org/2026.emnlp-main.157/
DOI:
Bibkey:
Cite (ACL):
Feng He, Hejia Wang, Linghao Meng, Ming Gao, and Qiankun Li. 2026. Verification Trap: Understanding Test-Time Selection Failures under False Premises in Code Generation. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 3613–3637, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Verification Trap: Understanding Test-Time Selection Failures under False Premises in Code Generation (He et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.157.pdf