Check for collisions in typ strings

Author: kroenlein

gemd/entity/dict_serializable.py

@@ -26,6 +26,9 @@ def __new__(mcs, name, bases, *args,
     def __init__(cls, name, bases, *args, typ: str = None, skip: Set[str] = frozenset(), **kwargs):
         super().__init__(name, bases, *args, **kwargs)
         if typ is not None:
+            if typ in cls._class and not issubclass(cls, cls._class.get(typ)):
+                raise ValueError(f"{cls} attempted to take typ {typ} from {cls._class.get(typ)}, "
+                                 f"which is not its ancestor.")
             cls.typ = typ
             cls._class[typ] = cls
         elif not hasattr(cls, "typ"):

gemd/entity/tests/test_entity.py

@@ -144,3 +144,21 @@ class TestConditionTemplate(
         pass
 
     TestConditionTemplate(name="Me", bounds=MolecularStructureBounds())
+
+
+def test_derived_collision():
+    """Test that an exception is thrown when multiple classes claim the same typ."""
+    # One parent
+    class Parent(DictSerializable, typ="mine"):
+        pass
+
+    # First kid is fine
+    class ElderChild(Parent, typ="mine"):
+        pass
+
+    # Mapping transferred
+    assert DictSerializable.class_mapping["mine"] is ElderChild
+
+    with pytest.raises(ValueError, match="mine"):
+        class SecondChild(Parent, typ="mine"):
+            pass