diff --git a/tests/testSetOps.py b/tests/testSetOps.py
index 2997472..c490509 100644
--- a/tests/testSetOps.py
+++ b/tests/testSetOps.py
@@ -82,6 +82,52 @@ def testPairs(self):
                     got = mass_weightedIntersection([(y, w2), (x, w1)])
                     self.assertEqual(expected, list(got.items()))
 
+    def testMany(self):
+        import random
+        N = 15  # number of IIBTrees to feed in
+        L = []
+        commonkey = N * 1000
+        allkeys = {commonkey: 1}
+        for i in range(N):
+            t = IIBTree()
+            t[commonkey] = i
+            for j in range(N-i):
+                key = i + j
+                allkeys[key] = 1
+                t[key] = N*i + j
+            L.append((t, i+1))
+        random.shuffle(L)
+        allkeys = allkeys.keys()
+        allkeys.sort()
+
+        # Test the union.
+        expected = []
+        for key in allkeys:
+            sum = 0
+            for t, w in L:
+                if t.has_key(key):
+                    sum += t[key] * w
+            expected.append((key, sum))
+        # print 'union', expected
+        got = mass_weightedUnion(L)
+        self.assertEqual(expected, list(got.items()))
+
+        # Test the intersection.
+        expected = []
+        for key in allkeys:
+            sum = 0
+            for t, w in L:
+                if t.has_key(key):
+                    sum += t[key] * w
+                else:
+                    break
+            else:
+                # We didn't break out of the loop so it's in the intersection.
+                expected.append((key, sum))
+        # print 'intersection', expected
+        got = mass_weightedIntersection(L)
+        self.assertEqual(expected, list(got.items()))
+
 def test_suite():
     return makeSuite(TestSetOps)