more human readable err msg and test

src/pymatgen/util/testing.py

@@ -79,16 +79,21 @@ def assert_msonable(obj: Any, test_is_subclass: bool = True) -> str:
         Returns:
             str: Serialized object.
         """
+        obj_name = obj.__class__.__name__
+
+        # Check if is an instance of MONable (or its subclasses)
         if test_is_subclass and not isinstance(obj, MSONable):
-            raise TypeError("obj is not MSONable")
+            raise TypeError(f"{obj_name} object is not MSONable")
 
+        # Check if the object can be accurately reconstructed from its dict representation
         if obj.as_dict() != type(obj).from_dict(obj.as_dict()).as_dict():
-            raise ValueError("obj could not be reconstructed accurately from its dict representation.")
+            raise ValueError(f"{obj_name} object could not be reconstructed accurately from its dict representation.")
 
+        # Verify that the deserialized object's class is a subclass of the original object's class
         json_str = json.dumps(obj.as_dict(), cls=MontyEncoder)
         round_trip = json.loads(json_str, cls=MontyDecoder)
         if not issubclass(type(round_trip), type(obj)):
-            raise TypeError(f"{type(round_trip)} != {type(obj)}")
+            raise TypeError(f"The reconstructed {round_trip.__class__.__name__} object is not a subclass of {obj_name}")
         return json_str
 
     @staticmethod

tests/util/test_testing.py

@@ -3,8 +3,10 @@
 import json
 import os
 from pathlib import Path
+from unittest.mock import patch
 
 import pytest
+from monty.json import MontyDecoder
 
 from pymatgen.core import Element, Structure
 from pymatgen.io.vasp.inputs import Kpoints
@@ -54,13 +56,6 @@ def test_creating_files_in_tmp_dir(self):
 
 
 class TestAssertMSONable(PymatgenTest):
-    """TODO:
-    - test: raise TypeError("obj is not MSONable")
-    - test: raise ValueError("obj could not be reconstructed accurately from its dict representation.")
-    - test: if not issubclass(type(round_trip), type(obj)):
-                raise TypeError(f"{type(round_trip)} != {type(obj)}")
-    """
-
     def test_valid_msonable(self):
         """Test a valid MSONable object."""
         kpts_obj = Kpoints.monkhorst_automatic((2, 2, 2), [0, 0, 0])
@@ -86,6 +81,43 @@ def test_valid_msonable(self):
 
         assert is_np_dict_equal(serialized, expected_result)
 
+    def test_non_msonable(self):
+        non_msonable = dict(hello="world")
+        # Test `test_is_subclass` is True
+        with pytest.raises(TypeError, match="dict object is not MSONable"):
+            self.assert_msonable(non_msonable)
+
+        # Test `test_is_subclass` is False (dict don't have `as_dict` method)
+        with pytest.raises(AttributeError, match="'dict' object has no attribute 'as_dict'"):
+            self.assert_msonable(non_msonable, test_is_subclass=False)
+
+    def test_cannot_reconstruct(self):
+        """Patch the `from_dict` method of `Kpoints` to return a corrupted object"""
+        kpts_obj = Kpoints.monkhorst_automatic((2, 2, 2), [0, 0, 0])
+
+        with patch.object(Kpoints, "from_dict", side_effect=lambda d: Kpoints(comment="Corrupted Object")):
+            reconstructed_obj = Kpoints.from_dict(kpts_obj.as_dict())
+            assert reconstructed_obj.comment == "Corrupted Object"
+
+            with pytest.raises(ValueError, match="Kpoints object could not be reconstructed accurately"):
+                self.assert_msonable(kpts_obj)
+
+    def test_not_round_trip(self):
+        kpts_obj = Kpoints.monkhorst_automatic((2, 2, 2), [0, 0, 0])
+
+        # Patch the MontyDecoder to return an object of a different class
+        class NotAKpoints:
+            pass
+
+        with patch.object(MontyDecoder, "process_decoded", side_effect=lambda d: NotAKpoints()) as mock_decoder:
+            with pytest.raises(
+                TypeError,
+                match="The reconstructed NotAKpoints object is not a subclass of Kpoints",
+            ):
+                self.assert_msonable(kpts_obj)
+
+            mock_decoder.assert_called()
+
 
 class TestPymatgenTest(PymatgenTest):
     def test_assert_str_content_equal(self):