Golang Test EOF after client.Do(req)

Question

I am using an application using the Gin framework. I am writing a test for one of my handlers:

package controllers

import (
    "bytes"
    "encoding/json"
    "github.com/gin-gonic/gin"
    "github.com/stretchr/testify/assert"
    "io/ioutil"
    "net/http"
    "net/http/httptest"
    ".x.x.x./driver/database/elastic"
    ".x.x.x./driver/database/mysql"
    ".x.x.x./driver/locale"
    ".x.x.x./driver/server/request/client"
    ".x.x.x./presenter/api/config"
    "testing"
)

func init() {
    config.Read()
    config.SetSentry()
    config.SetStructsDefaultTag("json")

    mysql.Setup()

    elastic.Setup()

    locale.Setup()
}

func TestClientBasketCtrl_AddItem(t *testing.T) {
    deviceId := "20b15b3f-8d8c-4a24-87c5-461a5d2bf0c8"
    userId := "0153783d-9971-4e4f-8cc3-3a3bc55d2268"
    serviceName := "payment"
    productId := "49f94d8f-5cdc-4325-9468-18b78e242130"
    count := uint(1)
    extra := "qqq"

    reqBody := client.BasketAddReq{
        DeviceId:    deviceId,
        UserId:      userId,
        ServiceName: serviceName,
        ProductId:   productId,
        Count:       count,
        Extra:       extra,
    }

    jsn, err := json.Marshal(reqBody)
    if err != nil {
        t.Fatalf("Error: %v", err)
    }

    ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        c, _ := gin.CreateTestContext(w)
        jsnTest, _ := json.Marshal(reqBody)
        r.Body = ioutil.NopCloser(bytes.NewReader(jsnTest))
        r.Header.Set("Content-Type", "application/json")
        c.Request = r
        new(ClientBasketCtrl).AddItem(c)
    }))
    defer ts.Close()

    clnt := &http.Client{}
    req, err := http.NewRequest(http.MethodPost, ts.URL, bytes.NewBuffer(jsn))
    req.Header.Set("Content-Type", "application/json")
    req.Close = true
    resp, err := clnt.Do(req)
    if err != nil { //HERE err HAPPENS
        t.Fatalf("Error: %v", err)
    }
    assert.Equal(t, http.StatusOK, resp.StatusCode)
}

The error seems to happen when you are not closing the request and I have added req.Close = true to the code but the error still remains. What's wrong with my code? I have mentioned by comments (//HERE err HAPPENS) that where the error happens. The err is like this (on the debugger).

err = {error | *url.Error}
   OP = {string} "POST"
   URL = {string} "http://127.0.0.1:41687"
   Err = {error | *errors.errorString} EOF
      s = {string} "EOF"