doReq := func(reqId string) {
		req, _ := NewRequest("GET", ts.URL, nil)
		trace := &httptrace.ClientTrace{
			GetConn: func(hostPort string) {
				preDial <- struct{}{}
			},
		}
		req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
		resp, err := tr.RoundTrip(req)
		if err != nil {
			t.Errorf("unexpected error for request %s: %v", reqId, err)
		}