diff --git a/Lib/test/test_capi.py b/Lib/test/test_capi.py
index eea41c1..17c4baf 100644
--- a/Lib/test/test_capi.py
+++ b/Lib/test/test_capi.py
@@ -2,9 +2,74 @@
 # these are all functions _testcapi exports whose name begins with 'test_'.
 
 import sys
+import time
+import random
+import unittest
+import threading
 from test import test_support
 import _testcapi
 
+class TestPendingCalls(unittest.TestCase):
+
+    def pendingcalls_submit(self, l, n):
+        def callback():
+            #this function can be interrupted by thread switching so let's
+            #use an atomic operation
+            l.append(None)
+
+        for i in range(n):
+            time.sleep(random.random()*0.02) #0.01 secs on average
+            #try submitting callback until successful.
+            #rely on regular interrupt to flush queue if we are
+            #unsuccessful.
+            while True:
+                if _testcapi._pending_threadfunc(callback):
+                    break;
+
+    def pendingcalls_wait(self, l, n):
+        #now, stick around until l[0] has grown to 10
+        count = 0;
+        while len(l) != n:
+            #this busy loop is where we expect to be interrupted to
+            #run our callbacks.  Note that callbacks are only run on the
+            #main thread
+            if False and test_support.verbose:
+                print "(%i)"%(len(l),),
+            for i in xrange(1000):
+                a = i*i
+            count += 1
+            self.failUnless(count < 10000,
+                "timeout waiting for %i callbacks, got %i"%(n, len(l)))
+        if False and test_support.verbose:
+            print "(%i)"%(len(l),)
+
+    def test_pendingcalls_threaded(self):
+        l = []
+
+        #do every callback on a separate thread
+        n = 32
+        threads = []
+        for i in range(n):
+            t = threading.Thread(target=self.pendingcalls_submit, args = (l, 1))
+            t.start()
+            threads.append(t)
+
+        self.pendingcalls_wait(l, n)
+
+        for t in threads:
+            t.join()
+
+    def test_pendingcalls_non_threaded(self):
+        #again, just using the main thread, likely they will all be dispathced at
+        #once.  It is ok to ask for too many, because we loop until we find a slot.
+        #the loop can be interrupted to dispatch.
+        #there are only 32 dispatch slots, so we go for twice that!
+        l = []
+        n = 64
+        self.pendingcalls_submit(l, n)
+        self.pendingcalls_wait(l, n)
+
+
 def test_main():
 
     for name in dir(_testcapi):
@@ -50,5 +115,7 @@
         t.start()
         t.join()
 
+    test_support.run_unittest(TestPendingCalls)
+
 if __name__ == "__main__":
     test_main()