'return snapshot value of stdout/stderr capturings.'

def readouterr(self):

    if hasattr(self, 'out'):
        out = self._readsnapshot(self.out.tmpfile)
    else:
        out = ''
    if hasattr(self, 'err'):
        err = self._readsnapshot(self.err.tmpfile)
    else:
        err = ''
    return [out, err]
