call site 8 for execnet.PopenGateway.exit
execnet/testing/test_gateway.py - line 517
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   def test_threads_twice():
       gw = py.execnet.PopenGateway()
       gw.remote_init_threads(3)
       py.test.raises(IOError, gw.remote_init_threads, 3)
->     gw.exit()