def METHOD_NAME(self):
    # ensure by default, distributed tracing is enabled
    adapter = Adapter()
    self.session.mount("mock", adapter)
    with self.tracer.trace("root") as root:
        def matcher(request):
            return self.headers_here(self.tracer, request, root)
        adapter.register_uri("GET", "mock://datadog/foo", additional_matcher=matcher, text="bar")
        resp = self.session.get("mock://datadog/foo")
        assert 200 == resp.status_code
        assert "bar" == resp.text