Fix bug where you could reassign class to another product type and create invalid relationships

src/ifcopenshell-python/test/api/root/test_reassign_class.py

@@ -0,0 +1,26 @@
+import test.bootstrap
+import ifcopenshell.api
+
+
+class TestReassignClass(test.bootstrap.IFC4):
+    def test_reassigning_a_simple_class(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        new = ifcopenshell.api.run("root.reassign_class", self.file, product=element, ifc_class="IfcSlab")
+        assert len([e for e in self.file]) == 1
+        assert new.id() == 2
+        assert new.is_a("IfcSlab")
+
+    def test_reassigning_a_predefined_type(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        new = ifcopenshell.api.run(
+            "root.reassign_class", self.file, product=element, ifc_class="IfcSlab", predefined_type="FLOOR"
+        )
+        assert new.PredefinedType == "FLOOR"
+
+    def test_falling_back_to_userdefined_if_the_predefined_type_cannot_be_reassigned(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        new = ifcopenshell.api.run(
+            "root.reassign_class", self.file, product=element, ifc_class="IfcSlab", predefined_type="FOO"
+        )
+        assert new.PredefinedType == "USERDEFINED"
+        assert new.ObjectType == "FOO"