def test_add_label_to_spans_abstract(self):
        tracer = base.Tracer()
        label_key = 'key'
        label_value = 'value'

        with self.assertRaises(NotImplementedError):
            tracer.add_label_to_spans(label_key, label_value)
    def test_list_collected_spans_abstract(self):
        tracer = base.Tracer()

        with self.assertRaises(NotImplementedError):
            tracer.list_collected_spans()
    def test_current_span_abstract(self):
        tracer = base.Tracer()

        with self.assertRaises(NotImplementedError):
            tracer.current_span()
    def test_end_trace_abstract(self):
        tracer = base.Tracer()

        with self.assertRaises(NotImplementedError):
            tracer.end_trace()