if err := requestMustFailWithRetryHeader(resultGot, http.StatusTooManyRequests); err != nil {
		t.Errorf("%s", err.Error())
	}
	resultGot = doer.Do(connReusingClient, shouldReuseConnection(t), "/echo?message=request-on-an-existing-connection-should-fail-with-429", time.Second)
	if err := requestMustFailWithRetryHeader(resultGot, http.StatusTooManyRequests); err != nil {