From 1489f0fde3cd4c4f9b3cdc35cc63c79de0672478 Mon Sep 17 00:00:00 2001
From: "Matthew W. Thompson" <mattwthompson@protonmail.com>
Date: Fri, 24 Jan 2025 17:07:51 -0600
Subject: [PATCH] TST: Add test for combining mixed 1-4 vdW and/or
 electrostatics

---
 .../unit_tests/operations/test_combine.py     | 47 +++++++++++++++----
 1 file changed, 38 insertions(+), 9 deletions(-)

diff --git a/openff/interchange/_tests/unit_tests/operations/test_combine.py b/openff/interchange/_tests/unit_tests/operations/test_combine.py
index 98cf27a00..1ea4e7c7e 100644
--- a/openff/interchange/_tests/unit_tests/operations/test_combine.py
+++ b/openff/interchange/_tests/unit_tests/operations/test_combine.py
@@ -6,10 +6,12 @@
 from openff.utilities.testing import skip_if_missing
 
 from openff.interchange import Interchange
+from openff.interchange._tests import MoleculeWithConformer
 from openff.interchange.drivers import get_openmm_energies
 from openff.interchange.exceptions import (
     CutoffMismatchError,
     SwitchingFunctionMismatchError,
+    UnsupportedCombinationError,
 )
 
 
@@ -19,8 +21,7 @@ def test_basic_combination(self, monkeypatch, sage_unconstrained):
         """Test basic use of Interchange.__add__() based on the README example"""
         monkeypatch.setenv("INTERCHANGE_EXPERIMENTAL", "1")
 
-        mol = Molecule.from_smiles("C")
-        mol.generate_conformers(n_conformers=1)
+        mol = MoleculeWithConformer.from_smiles("C")
         top = Topology.from_molecules([mol])
 
         interchange = Interchange.from_smirnoff(sage_unconstrained, top)
@@ -43,14 +44,10 @@ def test_basic_combination(self, monkeypatch, sage_unconstrained):
     def test_parameters_do_not_clash(self, monkeypatch, sage_unconstrained):
         monkeypatch.setenv("INTERCHANGE_EXPERIMENTAL", "1")
 
-        thf = Molecule.from_smiles("C1CCOC1")
-        ace = Molecule.from_smiles("CC(=O)O")
+        thf = MoleculeWithConformer.from_smiles("C1CCOC1")
+        ace = MoleculeWithConformer.from_smiles("CC(=O)O")
 
-        thf.generate_conformers(n_conformers=1)
-        ace.generate_conformers(n_conformers=1)
-
-        def make_interchange(molecule: Molecule) -> Interchange:
-            molecule.generate_conformers(n_conformers=1)
+        def make_interchange(molecule: MoleculeWithConformer) -> Interchange:
             interchange = Interchange.from_smirnoff(
                 force_field=sage_unconstrained,
                 topology=[molecule],
@@ -135,3 +132,35 @@ def test_error_mismatched_switching_function(
             sage.create_interchange(basic_top).combine(
                 sage_modified.create_interchange(basic_top),
             )
+
+    @pytest.mark.parametrize(
+        argnames=["vdw", "electrostatics"],
+        argvalues=[
+            (True, False),
+            (False, True),
+            (True, True),
+            (False, False),
+        ],
+    )
+    def test_dont_combine_mixed_14(self, sage, vdw, electrostatics):
+        """
+        Until it's implemented, error out when any non-bonded collections have non-equal 1-4 scaling factors.
+
+        See https://github.com/openforcefield/openff-interchange/issues/380
+
+        """
+        interchange1 = sage.create_interchange(MoleculeWithConformer.from_smiles("C").to_topology())
+        interchange2 = sage.create_interchange(MoleculeWithConformer.from_smiles("CCO").to_topology())
+
+        if vdw:
+            interchange2["vdW"].scale_14 = 0.444
+
+        if electrostatics:
+            interchange2["Electrostatics"].scale_14 = 0.444
+
+        if vdw or electrostatics:
+            with pytest.raises(UnsupportedCombinationError, match="1-4.*nonbond"):
+                interchange2.combine(interchange1)
+        else:
+            # if neither are modified, that error shouldn't be raised
+            interchange2.combine(interchange1)