add constraint check for recursion

test/test_db.py

@@ -10,7 +10,7 @@ from tinydb.storages import MemoryStorage
 
 from grung import examples
 from grung.db import GrungDB
-from grung.exceptions import PointerReferenceError, UniqueConstraintError
+from grung.exceptions import CircularReferenceError, UniqueConstraintError
 
 
 @pytest.fixture
@@ -49,13 +49,7 @@ def test_crud(db):
 
 
 def test_pointers(db):
-    user = examples.User(name="john", email="john@foo")
-    players = examples.Group(name="players", members=[user])
-
-    with pytest.raises(PointerReferenceError):
-        players = db.save(players)
-
-    user = db.save(user)
+    user = db.save(examples.User(name="john", email="john@foo"))
     players = db.save(examples.Group(name="players", members=[user]))
 
     user = db.table("User").get(doc_id=user.doc_id)
@@ -86,6 +80,11 @@ def test_subgroups(db):
     kirk = db.table("User").get(doc_id=kirk.doc_id)
     assert kirk.reference in unique_users
 
+    # recursion!
+    with pytest.raises(CircularReferenceError):
+        tos.members = [tos]
+        db.save(tos)
+
 
 def test_unique(db):
     user1 = examples.User(name="john", email="john@foo")