test add_site_property() ValueError msg

Author: janosh

pymatgen/core/structure.py

@@ -489,9 +489,12 @@ def add_site_property(self, property_name: str, values: Sequence | np.ndarray) -
             property_name (str): The name of the property to add.
             values (list): A sequence of values. Must be same length as
                 number of sites.
+
+        Raises:
+            ValueError: if len(values) != number of sites.
         """
         if len(values) != len(self):
-            raise ValueError(f"Values has length {len(values)} but there are {len(self)} sites! Must be same length.")
+            raise ValueError(f"{len(values)=} must equal sites in structure={len(self)}")
         for site, val in zip(self, values):
             site.properties[property_name] = val
 

tests/core/test_structure.py

@@ -2148,6 +2148,11 @@ def test_add_site_property(self):
         assert self.mol[0].charge == 4.1
         assert self.mol[0].magmom == 3
         self.mol.remove_site_property("magmom")
+
+        # test ValueError when values have wrong length
+        with pytest.raises(ValueError, match="len(values)=2 must equal sites in structure=5"):
+            self.mol.add_site_property("charge", [4, 2])
+
         with pytest.raises(AttributeError, match="attr='magmom' not found on Site"):
             _ = self.mol[0].magmom