Fix composition test

tests/utils/test_additive.py

@@ -10,7 +10,10 @@
 from metatrain.utils.additive import ZBL, CompositionModel, remove_additive
 from metatrain.utils.data import Dataset, DatasetInfo
 from metatrain.utils.data.readers import read_systems, read_targets
-from metatrain.utils.data.target_info import get_energy_target_info
+from metatrain.utils.data.target_info import (
+    get_energy_target_info,
+    get_generic_target_info,
+)
 from metatrain.utils.neighbor_lists import (
     get_requested_neighbor_lists,
     get_system_with_neighbor_lists,
@@ -369,23 +372,33 @@ def test_composition_model_missing_types():
 
 def test_composition_model_wrong_target():
     """
-    Test the error when a non-energy is fed to the composition model.
+    Test the error when a non-scalar is fed to the composition model.
     """
+    composition_model = CompositionModel(
+        model_hypers={},
+        dataset_info=DatasetInfo(
+            length_unit="angstrom",
+            atomic_types=[1],
+            targets={
+                "force": get_generic_target_info(
+                    {
+                        "quantity": "force",
+                        "unit": "",
+                        "type": {"cartesian": {"rank": 1}},
+                        "num_properties": 1,
+                        "per_atom": True,
+                    }
+                )
+            },
+        ),
+    )
+    # This should do nothing, because the target is not scalar and it should be
+    # ignored by the composition model. The warning is due to the "empty" dataset
+    # not containing H (atomic type 1)
+    with pytest.warns(UserWarning, match="do not contain atomic types"):
+        composition_model.train_model([])
 
-    with pytest.raises(
-        ValueError,
-        match="only supports energy-like outputs",
-    ):
-        CompositionModel(
-            model_hypers={},
-            dataset_info=DatasetInfo(
-                length_unit="angstrom",
-                atomic_types=[1],
-                targets={
-                    "energy": get_energy_target_info({"quantity": "force", "unit": ""})
-                },
-            ),
-        )
+    assert composition_model.weights.shape == (0, 1)
 
 
 def test_zbl():