func (rw *ResponseRecorder) Header() http.Header {
	m := rw.HeaderMap
	if m == nil {
		m = make(http.Header)
		rw.HeaderMap = m
	}
	return m
}
Header returns the response headers.
package httptest
import (
	"bytes"
	"fmt"
	"io/ioutil"
	"net/http"
	"strconv"
	"strings"
	"golang.org/x/net/http/httpguts"
)
type ResponseRecorder struct {
	Code int
	HeaderMap http.Header
	Body *bytes.Buffer
	Flushed bool
	result      *http.Response  
	snapHeader  http.Header     
	wroteHeader bool
}
func NewRecorder() *ResponseRecorder {
	return &ResponseRecorder{
		HeaderMap: make(http.Header),
		Body:      new(bytes.Buffer),
		Code:      200,
	}
}
const DefaultRemoteAddr = "1.2.3.4"