test(common): add regression for atom type remap (#5050)

## Summary
- add a regression test that reproduces the original atom-type remapping
failure when the training system contains fewer atom types than the
provided type_map
- ensure the fix from commit 4ec0437
remains covered going forward

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Tests**
* Added unit tests for DeepmdData that validate atom-type remapping,
handling of unused types, and correct loading/formatting of type arrays.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: OutisLi

source/tests/common/test_deepmd_data.py

@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: LGPL-3.0-or-later
+import tempfile
+import unittest
+from pathlib import (
+    Path,
+)
+
+import numpy as np
+
+from deepmd.utils.data import (
+    DeepmdData,
+)
+
+
+class TestDeepmdDataTypeMap(unittest.TestCase):
+    def setUp(self) -> None:
+        self.tmpdir = tempfile.TemporaryDirectory()
+        self.root = Path(self.tmpdir.name)
+        self.set_dir = self.root / "set.000"
+        self.set_dir.mkdir()
+
+        # minimal required dataset
+        atom_types = np.array([0, 1, 0, 1], dtype=np.int32)
+        np.savetxt(self.root / "type.raw", atom_types, fmt="%d")
+        np.savetxt(
+            self.root / "type_map.raw",
+            np.array(["O", "H", "Si"], dtype=object),
+            fmt="%s",
+        )
+
+        coord = np.zeros((1, atom_types.size * 3), dtype=np.float32)
+        box = np.eye(3, dtype=np.float32).reshape(1, 9)
+        np.save(self.set_dir / "coord.npy", coord)
+        np.save(self.set_dir / "box.npy", box)
+
+    def tearDown(self) -> None:
+        self.tmpdir.cleanup()
+
+    def test_remap_with_unused_types(self) -> None:
+        data = DeepmdData(str(self.root), type_map=["H", "O", "Si"])
+
+        expected_atom_types = np.array([1, 0, 1, 0], dtype=np.int32)
+        np.testing.assert_array_equal(data.atom_type, expected_atom_types)
+        self.assertEqual(data.type_map, ["H", "O", "Si"])
+
+        loaded = data._load_set(self.set_dir)
+        expected_sorted = expected_atom_types[data.idx_map]
+        np.testing.assert_array_equal(loaded["type"], np.tile(expected_sorted, (1, 1)))