fix: address remaining reviewer comments

- test_change_bias: assert full bias tensor shape, not just first 2 values
- test_dp_freeze: clarify NoPBC test compares independent implementations

Author: Han Wang

source/tests/pt_expt/test_change_bias.py

@@ -312,7 +312,8 @@ def test_change_bias_frozen_pt2_user_defined(self) -> None:
         updated_model = BaseModel.deserialize(updated_data["model"])
         updated_bias = to_numpy(updated_model.get_out_bias())
 
-        np.testing.assert_allclose(updated_bias.flatten()[:2], [1.0, 2.0], atol=1e-10)
+        expected = np.array([[1.0], [2.0]])
+        np.testing.assert_allclose(updated_bias, expected, atol=1e-10)
 
     def test_change_bias_pt2_pte_consistency(self) -> None:
         """Change-bias on .pte and .pt2 should produce same bias values."""

source/tests/pt_expt/test_dp_freeze.py

@@ -161,6 +161,9 @@ def test_freeze_pt2_nopbc_negative_coords(self) -> None:
 
         Regression test: the C++ NoPBC path creates a fake box and must
         shift coordinates so atoms with negative values are inside [0, L).
+        Compares .pt2 (C++ fake-box path) against .pte (Python no-ghost path)
+        — these are independent NoPBC implementations so cross-comparison
+        validates both.
         """
         import numpy as np