Fix tests

Author: gpahal

tests/test_txn.py

@@ -328,8 +328,8 @@ def test_mutate_conflict(self):
 
         txn2.commit()
 
-        with self.assertRaises(pydgraph.AbortedError):
-            _ = txn.mutate(set_obj={'uid': uid, 'name': 'Manish2'})
+        _ = txn.mutate(set_obj={'uid': uid, 'name': 'Manish2'})
+        self.assertRaises(pydgraph.AbortedError, txn.commit)
 
     def test_conflict_ignore(self):
         """Tests a mutation with ignore index conflict."""