var cancel context.CancelFunc
			ctx, cancel = context.WithTimeout(req.Context(), timeout)
			defer cancel()

			req = req.WithContext(ctx)
		}

		// setup trace
		trace := &httptrace.ClientTrace{
			GotConn: func(connInfo httptrace.GotConnInfo) {
				callback(connInfo)
			},
		}
		req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))

		response, err := client.Do(req)

			if v, ok := header[h]; ok {
				t.Errorf("%s is %q; must not be sent", h, v)
			}
		}
	}

	var respCounter uint8
	trace := &httptrace.ClientTrace{
		Got1xxResponse: func(code int, header textproto.MIMEHeader) error {
			switch respCounter {
			case 0:

				}
				return false
			}
			return true
		})
		conns := 0
		var info httptrace.GotConnInfo
		ctx := httptrace.WithClientTrace(context.Background(), &httptrace.ClientTrace{
			GotConn: func(v httptrace.GotConnInfo) {
				conns++
				info = v
			},
		})
		req, err := NewRequestWithContext(ctx, "GET", cst.ts.URL, nil)
		if err != nil {
			t.Fatal(err)
		}