To overcome the limitations of first-session adaptation (FSA), an efficient strategy to integrate large pre-trained models (PTMs) into class incremental learning (CIL), this paper presents a plasticity-enhanced test-time adaptation (PLASTIC) method. PLASTIC leverages test-time adaptation (TTA) to dynamically fine-tune layer regularization (LayerNorm) parameters on unlabeled test data, thereby enhancing adaptability to evolving tasks and improving robustness to data corruption. A teacher-student distillation framework prevents model variance caused by TTA and maintains stable learning. Experimental results on various benchmarks show that PLASTIC outperforms existing and state-of-the-art PTM-based CIL approaches, while also demonstrating robustness to data corruption.