def test_start(self):
    span_name = 'root_span'
    span = self._make_one(span_name)
    self.assertIsNone(span.start_time)
    span.start()
    self.assertIsNone(span.start_time)
def test_start(self):
    span_name = 'root_span'
    span = self._make_one(span_name)
    self.assertIsNone(span.start_time)
    span.start()
    self.assertIsNone(span.start_time)