Add a small test (#2133)

src/quacc/calculators/vasp/params.py

@@ -398,11 +398,11 @@ def __init__(
         -------
         None
         """
+        if atoms is None and prev_dir is None:
+            raise ValueError("Either atoms or prev_dir must be provided.")
         self.atoms = atoms
         self.prev_dir = prev_dir
         self.structure = AseAtomsAdaptor.get_structure(atoms)
-        if atoms is None and prev_dir is None:
-            raise ValueError("Either atoms or prev_dir must be provided.")
 
     def convert_dict_set(self, dict_set: DictSet) -> dict:
         """

tests/core/calculators/vasp/test_vasp.py

@@ -816,6 +816,11 @@ def test_preset_override():
     assert calc.parameters.get("efermi") is None
 
 
+def test_bad_pmg_converter():
+    with pytest.raises(ValueError, match="Either atoms or prev_dir must be provided"):
+        MPtoASEConverter()
+
+
 def test_pmg_input_set():
     atoms = bulk("Cu")
     parameters = MPtoASEConverter(atoms=atoms).convert_dict_set(MPRelaxSet)