import unittest


class TestCase(unittest.TestCase):
    
        
    def testTracing(self):
        
        def f1(cb):
            return cb()
            
        def f2():
            return f1(f2) #call myself and go past the recursion limit
        
        def pass_call():
            pass
        
        class Tracer(object):
            
            def __init__(self):
                self.trace = 0

            def trace_func(self, frame, event, arg):
                self.trace += 1
                return self.trace_func
            

        tracer = Tracer()
        import sys
        sys.settrace(tracer.trace_func)
        
        try:
            initial = tracer.trace
            pass_call()
            self.assertEqual(3, tracer.trace - initial)
            
            try:
                f2()
            except RuntimeError as e:
                self.assert_('recursion' in str(e))
            else:
                self.fail('Expected recursion error!')
            initial = tracer.trace
            pass_call()
            self.assertEqual(3, tracer.trace - initial)
        finally:
            sys.settrace(None)
        
if __name__ == '__main__':
    unittest.main()