add TestMolecule.test_from_sites

document raises ValueError on empty sites in from_sites doc str

Author: janosh

pymatgen/core/structure.py

@@ -942,11 +942,14 @@ def from_sites(
                 Will be serialized when writing the structure to JSON or YAML but is
                 lost when converting to other formats.
 
+        Raises:
+            ValueError: If sites is empty or sites do not have the same lattice.
+
         Returns:
             (Structure) Note that missing properties are set as None.
         """
         if len(sites) < 1:
-            raise ValueError(f"You need at least one site to construct a {cls}")
+            raise ValueError(f"You need at least 1 site to construct a {cls.__name__}")
         prop_keys: list[str] = []
         props = {}
         labels = [site.label for site in sites]
@@ -2996,7 +2999,15 @@ def from_sites(
                 to True.
             properties (dict): dictionary containing properties associated
                 with the whole molecule.
+
+        Raises:
+            ValueError: If sites is empty
+
+        Returns:
+            Molecule
         """
+        if len(sites) < 1:
+            raise ValueError(f"You need at least 1 site to make a {cls.__name__}")
         props = collections.defaultdict(list)
         for site in sites:
             for k, v in site.properties.items():

tests/core/test_structure.py

@@ -1392,6 +1392,9 @@ def test_from_sites(self):
         struct = Structure.from_sites(self.struct, to_unit_cell=True)
         assert struct.site_properties["hello"][1] == 2
 
+        with pytest.raises(ValueError, match="You need at least 1 site to construct a Structure"):
+            Structure.from_sites([])
+
     def test_charge(self):
         struct = Structure.from_sites(self.struct)
         assert struct.charge == 0, "Initial Structure not defaulting to behavior in SiteCollection"
@@ -1943,6 +1946,13 @@ def test_insert_remove_append(self):
         mol.remove_sites([0, 1])
         assert mol.formula == "H3 N1"
 
+    def test_from_sites(self):
+        mol = Molecule.from_sites(self.mol)
+        assert mol == self.mol
+
+        with pytest.raises(ValueError, match="You need at least 1 site to make a Molecule"):
+            Molecule.from_sites([])
+
     def test_translate_sites(self):
         self.mol.translate_sites([0, 1], [0.5, 0.5, 0.5])
         assert_array_equal(self.mol.cart_coords[0], [0.5, 0.5, 0.5])