// and wait for the order to proceed.
				ch := make(chan struct{})
				putidlec <- ch
				close(putidlec) // panic if PutIdleConn runs twice for some reason
				<-ch
			},
		})
		req, _ := NewRequestWithContext(ctx, "GET", ts.URL, nil)
		res, err := client.Do(req)
		if err != nil {
			reqerrc <- err
		} else {
			res.Body.Close()
		}
	}()