def METHOD_NAME(self, tmpdir):
    mh = ModifyHeaders()
    with taddons.context(mh) as tctx:
        tmpfile = tmpdir.join("replacement")
        tmpfile.write("two")
        tctx.configure(mh, modify_headers=["/~q/one/@" + str(tmpfile)])
        f = tflow.tflow()
        f.request.headers["one"] = "xxx"
        mh.request(f)
        assert f.request.headers["one"] == "two"