diff --git a/src/tests/testStatebag.py b/src/tests/testStatebag.py
--- a/src/tests/testStatebag.py
+++ b/src/tests/testStatebag.py
@@ -1,3 +1,4 @@
+import random
 import os.path
 from unittest import TestCase
 
@@ -6,7 +7,7 @@ from util import BLACK as B,WHITE as W,E
 from go.engine import SpecGo,Engine
 import go.engine
 from statebag import BoardState,StateBag,updateDiff
-from .util import simpleLoadSgf,listStates
+from .util import simpleLoadSgf,listBoards,listStates
 
 
 class TestBoardState(TestCase):
@@ -69,21 +70,47 @@ class TestBoardState(TestCase):
 
 
 class TestStateBag(TestCase):
-	def testReal(self):
+	def testSkips(self):
 		go.engine.eng=Engine()
 		files=["O-Takao-20110106.sgf","Sakai-Iyama-20110110.sgf"]
 
 		for f in files:
 			moves=simpleLoadSgf(os.path.join(cfg.srcDir,"tests/data",f))
-			states=listStates(moves)
+			boards=listBoards(moves)
 
 			for k in range(1,3):
 				bag=StateBag()
 				i=0
-				for s_ in states:
+				for b in boards:
 					i+=1
 					if i%(2*k-1)>=k: # keep k, skip k-1
 						continue
-					s=bag.pushState(s_)
+					s=bag.pushState(b)
 					if len(bag._states)>1:
 						self.assertIs(s.getPrev(), bag._states[-2])
+
+	def testNoise(self):
+		random.seed(361)
+		go.engine.eng=Engine()
+		files=["O-Takao-20110106.sgf","Sakai-Iyama-20110110.sgf"]
+
+		for f in files:
+			moves=simpleLoadSgf(os.path.join(cfg.srcDir,"tests/data",f))
+			boards=listBoards(moves)
+
+			bag=StateBag()
+			for b in boards:
+				s=bag.pushState(b)
+				if len(bag._states)>1:
+					# correct state skipping the erroneous one, connected to the previous correct one
+					self.assertIs(s.getPrev(), bag._states[key])
+
+				if random.random()<0.9:
+					key=-2
+					continue
+				for i in range(random.randrange(1,10)):
+					r=random.randrange(19)
+					c=random.randrange(19)
+					b[r][c]=(b[r][c]+random.choice((2,3)))%3-1 # random transformation [-1,1]->[-1,1]
+				bag.pushState(b)
+				key=-3