call site 2 for io.StdCapture.call
log/testing/test_log.py - line 110
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   def test_log_stderr(self):
       py.log.setconsumer("default", py.log.STDERR) 
->     res, out, err = callcapture(py.log.default, "hello")
       assert not out
       assert err.strip() == '[default] hello'