diff --git a/hb/valid.md b/hb/valid.md
new file mode 100644
index 0000000..68054c6
--- /dev/null
+++ b/hb/valid.md
@@ -0,0 +1,816 @@
+// File: hb/go.mod
+```go
+module hb
+
+go 1.21
+```
+
+// File: hb/types.go
+```go
+package hb
+
+// RefundRequest 退款接口请求参数
+type RefundRequest struct {
+	MerchantId   string `json:"merchantId"`             // 商户编号
+	RequestId    string `json:"requestId"`              // 商户请求号
+	SignType     string `json:"signType"`               // 签名方式：MD5 或 RSA
+	Type         string `json:"type"`                   // 接口类型：OrderRefund
+	Version      string `json:"version"`                // 版本号：2.0.0
+	OrderId      string `json:"orderId"`                // 商户订单号
+	Amount       string `json:"amount"`                 // 退款金额，以分为单位
+	MerchantCert string `json:"merchantCert,omitempty"` // 商户证书公钥（不参与签名）
+	Hmac         string `json:"hmac,omitempty"`         // 签名数据
+}
+
+// RefundResponse 退款接口响应参数
+type RefundResponse struct {
+	MerchantId string `json:"merchantId"`             // 商户编号
+	PayNo      string `json:"payNo"`                  // 手机支付平台退款交易流水号
+	ReturnCode string `json:"returnCode"`             // 返回码
+	Message    string `json:"message"`                // 返回码描述信息
+	SignType   string `json:"signType"`               // 签名方式：MD5 或 RSA
+	Type       string `json:"type"`                   // 接口类型：OrderRefund
+	Version    string `json:"version"`                // 版本号：2.0.0
+	Amount     string `json:"amount"`                 // 退款金额，单位为分
+	OrderId    string `json:"orderId"`                // 商户订单号
+	Status     string `json:"status"`                 // 退款结果：SUCCESS / FAILED
+	ServerCert string `json:"serverCert,omitempty"`   // 服务器证书公钥（不参与签名）
+	Hmac       string `json:"hmac,omitempty"`         // 签名数据
+}
+
+// RefundStatus 退款状态常量
+const (
+	RefundStatusSuccess = "SUCCESS"
+	RefundStatusFailed  = "FAILED"
+)
+
+// SignType 签名方式常量
+const (
+	SignTypeMD5 = "MD5"
+	SignTypeRSA = "RSA"
+)
+
+// 接口类型常量
+const (
+	InterfaceTypeOrderRefund = "OrderRefund"
+)
+
+// 版本号常量
+const (
+	Version = "2.0.0"
+)
+
+// 返回码常量
+const (
+	ReturnCodeSuccess    = "000000"
+	ReturnCodeSuccessAlt = "MCG00000"
+)
+```
+
+// File: hb/errors.go
+```go
+package hb
+
+import "fmt"
+
+// Error 自定义错误类型
+type Error struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
+	Err     error  `json:"-"`
+}
+
+func (e *Error) Error() string {
+	if e.Err != nil {
+		return fmt.Sprintf("[%s] %s: %v", e.Code, e.Message, e.Err)
+	}
+	return fmt.Sprintf("[%s] %s", e.Code, e.Message)
+}
+
+func (e *Error) Unwrap() error {
+	return e.Err
+}
+
+// NewError 创建新的错误
+func NewError(code, message string, err error) *Error {
+	return &Error{
+		Code:    code,
+		Message: message,
+		Err:     err,
+	}
+}
+
+// 预定义错误
+var (
+	ErrSignTypeInvalid    = NewError("SIGN_TYPE_INVALID", "不支持的签名方式，仅支持 MD5 或 RSA", nil)
+	ErrSignVerifyFailed   = NewError("SIGN_VERIFY_FAILED", "签名验证失败", nil)
+	ErrPrivateKeyInvalid  = NewError("PRIVATE_KEY_INVALID", "私钥格式无效", nil)
+	ErrPublicKeyInvalid   = NewError("PUBLIC_KEY_INVALID", "公钥格式无效", nil)
+	ErrNetwork            = NewError("NETWORK_ERROR", "网络请求失败", nil)
+	ErrResponseParse      = NewError("RESPONSE_PARSE_ERROR", "响应解析失败", nil)
+	ErrMerchantIdEmpty    = NewError("MERCHANT_ID_EMPTY", "商户编号不能为空", nil)
+	ErrSignKeyEmpty       = NewError("SIGN_KEY_EMPTY", "商户密钥不能为空", nil)
+	ErrRequestIdEmpty     = NewError("REQUEST_ID_EMPTY", "商户请求号不能为空", nil)
+	ErrOrderIdEmpty       = NewError("ORDER_ID_EMPTY", "商户订单号不能为空", nil)
+	ErrAmountEmpty        = NewError("AMOUNT_EMPTY", "退款金额不能为空", nil)
+)
+
+// 错误码映射
+var ErrorCodeMap = map[string]string{
+	"C01088": "退货金额域非法",
+	"C01081": "产品名称域越界",
+	"C01033": "产品名称域为空",
+	"C01030": "有效期单位域不合法",
+	"C01028": "有效期数量域为0",
+	"C01027": "有效期数量域为空",
+	"C01025": "订单日期域不合法",
+	"C01024": "订单日期域为空",
+	"C01019": "币种域取值不合法",
+	"C01018": "币种域为空",
+	"C01014": "订单金额域为空",
+	"D99981": "订单已过期",
+	"D23190": "退款日期超过最大有效期",
+	"D22407": "退款金额大于可退款金额",
+	"D22401": "退货金额大于可退货金额",
+	"D22208": "订单状态异常",
+	"D22201": "订单不存在",
+	"D22224": "账户支付方式不正确",
+	"D77040": "商户没有开通此类交易的权限",
+	"IPS0008": "签名不符，一般都是由于中文编码引起",
+	"IPS0001": "一般都是因为商户编号或者密钥不对引起",
+}
+
+// GetErrorDescription 根据错误码获取错误描述
+func GetErrorDescription(code string) string {
+	if desc, ok := ErrorCodeMap[code]; ok {
+		return desc
+	}
+	return "未知错误码"
+}
+```
+
+// File: hb/crypto.go
+```go
+package hb
+
+import (
+	"crypto"
+	"crypto/md5"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha1"
+	"crypto/x509"
+	"encoding/hex"
+	"encoding/pem"
+	"fmt"
+	"strings"
+)
+
+// buildSignString 按文档指定顺序拼接签名串（请求）
+// 参数顺序：merchantId, requestId, signType, type, version, orderId, amount
+func buildSignString(params map[string]string, orderedKeys []string) string {
+	var parts []string
+	for _, k := range orderedKeys {
+		if v, ok := params[k]; ok {
+			parts = append(parts, fmt.Sprintf("%s=%s", k, v))
+		}
+	}
+	return strings.Join(parts, "&")
+}
+
+// getRequestSignKeys 获取请求签名参数顺序
+func getRequestSignKeys() []string {
+	return []string{"merchantId", "requestId", "signType", "type", "version", "orderId", "amount"}
+}
+
+// getResponseSignKeys 获取响应签名参数顺序
+func getResponseSignKeys() []string {
+	return []string{"merchantId", "payNo", "returnCode", "message", "signType", "type", "version", "amount", "orderId", "status"}
+}
+
+// SignMD5 MD5签名
+// 在待签名数据之后加上商户密钥（signKey），生成MD5摘要
+func SignMD5(signStr, signKey string) string {
+	data := signStr + signKey
+	hash := md5.Sum([]byte(data))
+	return hex.EncodeToString(hash[:])
+}
+
+// VerifyMD5 验证MD5签名
+func VerifyMD5(signStr, signKey, hmac string) bool {
+	return SignMD5(signStr, signKey) == hmac
+}
+
+// SignRSA RSA签名（配合SHA-1）
+// 使用商户私钥对签名串进行RSA-SHA1签名
+func SignRSA(signStr string, privateKeyPEM string) (string, error) {
+	block, _ := pem.Decode([]byte(privateKeyPEM))
+	if block == nil {
+		return "", fmt.Errorf("failed to decode PEM private key")
+	}
+
+	var privateKey *rsa.PrivateKey
+
+	// 尝试PKCS8格式
+	key, err := x509.ParsePKCS8PrivateKey(block.Bytes)
+	if err == nil {
+		var ok bool
+		privateKey, ok = key.(*rsa.PrivateKey)
+		if !ok {
+			return "", fmt.Errorf("not a RSA private key")
+		}
+	} else {
+		// 尝试PKCS1格式
+		privateKey, err = x509.ParsePKCS1PrivateKey(block.Bytes)
+		if err != nil {
+			return "", fmt.Errorf("failed to parse private key (PKCS1/PKCS8): %v", err)
+		}
+	}
+
+	// 计算SHA-1哈希
+	hash := sha1.Sum([]byte(signStr))
+
+	// RSA签名
+	signature, err := rsa.SignPKCS1v15(rand.Reader, privateKey, crypto.SHA1, hash[:])
+	if err != nil {
+		return "", fmt.Errorf("RSA sign failed: %v", err)
+	}
+
+	return hex.EncodeToString(signature), nil
+}
+
+// VerifyRSA 验证RSA签名
+// 使用手机支付公钥验证响应签名
+func VerifyRSA(signStr, signatureHex, publicKeyPEM string) error {
+	block, _ := pem.Decode([]byte(publicKeyPEM))
+	if block == nil {
+		return fmt.Errorf("failed to decode PEM public key")
+	}
+
+	// 尝试解析公钥
+	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
+	if err != nil {
+		// 尝试解析证书
+		cert, err := x509.ParseCertificate(block.Bytes)
+		if err != nil {
+			return fmt.Errorf("failed to parse public key: %v", err)
+		}
+		pub = cert.PublicKey
+	}
+
+	rsaPub, ok := pub.(*rsa.PublicKey)
+	if !ok {
+		return fmt.Errorf("not a RSA public key")
+	}
+
+	// 解码签名
+	signature, err := hex.DecodeString(signatureHex)
+	if err != nil {
+		return fmt.Errorf("failed to decode signature hex: %v", err)
+	}
+
+	// 计算SHA-1哈希
+	hash := sha1.Sum([]byte(signStr))
+
+	// 验证签名
+	err = rsa.VerifyPKCS1v15(rsaPub, crypto.SHA1, hash[:], signature)
+	if err != nil {
+		return fmt.Errorf("RSA verify failed: %v", err)
+	}
+
+	return nil
+}
+
+// extractCertFromPEM 从PEM格式的证书中提取公钥PEM
+// 有些场景下serverCert返回的是证书，需要提取公钥
+func extractPublicKeyFromCert(certPEM string) (string, error) {
+	block, _ := pem.Decode([]byte(certPEM))
+	if block == nil {
+		return "", fmt.Errorf("failed to decode PEM certificate")
+	}
+
+	cert, err := x509.ParseCertificate(block.Bytes)
+	if err != nil {
+		return "", fmt.Errorf("failed to parse certificate: %v", err)
+	}
+
+	pubKeyBytes, err := x509.MarshalPKIXPublicKey(cert.PublicKey)
+	if err != nil {
+		return "", fmt.Errorf("failed to marshal public key: %v", err)
+	}
+
+	pubKeyPEM := pem.EncodeToMemory(&pem.Block{
+		Type:  "PUBLIC KEY",
+		Bytes: pubKeyBytes,
+	})
+
+	return string(pubKeyPEM), nil
+}
+```
+
+// File: hb/client.go
+```go
+package hb
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+// Client 手机支付平台客户端
+type Client struct {
+	merchantId    string   // 商户编号
+	signKey       string   // 商户密钥（MD5签名使用）
+	privateKeyPEM string   // 商户RSA私钥（RSA签名使用）
+	baseURL       string   // 接口基础URL
+	httpClient    *http.Client
+}
+
+// ClientOption 客户端配置选项
+type ClientOption func(*Client)
+
+// WithSignKey 设置MD5签名密钥
+func WithSignKey(signKey string) ClientOption {
+	return func(c *Client) {
+		c.signKey = signKey
+	}
+}
+
+// WithPrivateKey 设置RSA私钥（PEM格式）
+func WithPrivateKey(privateKeyPEM string) ClientOption {
+	return func(c *Client) {
+		c.privateKeyPEM = privateKeyPEM
+	}
+}
+
+// WithBaseURL 设置接口基础URL
+func WithBaseURL(baseURL string) ClientOption {
+	return func(c *Client) {
+		c.baseURL = baseURL
+	}
+}
+
+// WithHTTPClient 设置自定义HTTP客户端
+func WithHTTPClient(httpClient *http.Client) ClientOption {
+	return func(c *Client) {
+		c.httpClient = httpClient
+	}
+}
+
+// NewClient 创建新的手机支付平台客户端
+// merchantId: 商户编号
+// opts: 配置选项
+func NewClient(merchantId string, opts ...ClientOption) (*Client, error) {
+	if merchantId == "" {
+		return nil, ErrMerchantIdEmpty
+	}
+
+	c := &Client{
+		merchantId: merchantId,
+		baseURL:    "https://ipos.10086.cn",
+		httpClient: &http.Client{},
+	}
+
+	for _, opt := range opts {
+		opt(c)
+	}
+
+	return c, nil
+}
+
+// Refund 退款接口
+// 通过中国移动手机支付渠道，将已成功交易的款项退还给用户
+func (c *Client) Refund(ctx context.Context, req *RefundRequest) (*RefundResponse, error) {
+	if req == nil {
+		return nil, fmt.Errorf("request cannot be nil")
+	}
+
+	// 设置固定参数
+	req.MerchantId = c.merchantId
+	req.Type = InterfaceTypeOrderRefund
+	req.Version = Version
+
+	// 参数校验
+	if req.RequestId == "" {
+		return nil, ErrRequestIdEmpty
+	}
+	if req.OrderId == "" {
+		return nil, ErrOrderIdEmpty
+	}
+	if req.Amount == "" {
+		return nil, ErrAmountEmpty
+	}
+	if req.SignType == "" {
+		return nil, ErrSignTypeInvalid
+	}
+	if req.SignType != SignTypeMD5 && req.SignType != SignTypeRSA {
+		return nil, ErrSignTypeInvalid
+	}
+
+	// 生成签名
+	hmac, err := c.generateRequestSign(req)
+	if err != nil {
+		return nil, fmt.Errorf("generate sign failed: %w", err)
+	}
+	req.Hmac = hmac
+
+	// 构建请求参数
+	params := c.buildRequestParams(req)
+
+	// 发送请求
+	resp, err := c.doPost(ctx, params)
+	if err != nil {
+		return nil, err
+	}
+
+	// 验证响应签名
+	if err := c.verifyResponseSign(resp); err != nil {
+		return nil, err
+	}
+
+	return resp, nil
+}
+
+// generateRequestSign 生成请求签名
+func (c *Client) generateRequestSign(req *RefundRequest) (string, error) {
+	// 构建参数字典
+	params := map[string]string{
+		"merchantId": req.MerchantId,
+		"requestId":  req.RequestId,
+		"signType":   req.SignType,
+		"type":       req.Type,
+		"version":    req.Version,
+		"orderId":    req.OrderId,
+		"amount":     req.Amount,
+	}
+
+	// 按文档指定顺序拼接签名串
+	signStr := buildSignString(params, getRequestSignKeys())
+
+	switch req.SignType {
+	case SignTypeMD5:
+		if c.signKey == "" {
+			return "", ErrSignKeyEmpty
+		}
+		return SignMD5(signStr, c.signKey), nil
+	case SignTypeRSA:
+		if c.privateKeyPEM == "" {
+			return "", ErrPrivateKeyInvalid
+		}
+		return SignRSA(signStr, c.privateKeyPEM)
+	default:
+		return "", ErrSignTypeInvalid
+	}
+}
+
+// buildRequestParams 构建请求参数（用于HTTP请求）
+func (c *Client) buildRequestParams(req *RefundRequest) url.Values {
+	params := url.Values{}
+	params.Set("merchantId", req.MerchantId)
+	params.Set("requestId", req.RequestId)
+	params.Set("signType", req.SignType)
+	params.Set("type", req.Type)
+	params.Set("version", req.Version)
+	params.Set("orderId", req.OrderId)
+	params.Set("amount", req.Amount)
+	params.Set("hmac", req.Hmac)
+	return params
+}
+
+// doPost 发送POST请求
+func (c *Client) doPost(ctx context.Context, params url.Values) (*RefundResponse, error) {
+	apiURL := c.baseURL + "/ips/cmpayService"
+
+	bodyStr := params.Encode()
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, strings.NewReader(bodyStr))
+	if err != nil {
+		return nil, fmt.Errorf("create request failed: %w", err)
+	}
+
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded; charset=utf-8")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("do request failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("read response body failed: %w", err)
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("unexpected status code: %d, body: %s", resp.StatusCode, string(body))
+	}
+
+	return parseResponse(string(body))
+}
+
+// parseResponse 解析响应字符串为结构体
+func parseResponse(raw string) (*RefundResponse, error) {
+	resp := &RefundResponse{}
+
+	pairs := strings.Split(raw, "&")
+	for _, pair := range pairs {
+		eqIdx := strings.IndexByte(pair, '=')
+		if eqIdx < 0 {
+			continue
+		}
+		key := pair[:eqIdx]
+		value := pair[eqIdx+1:]
+
+		switch key {
+		case "merchantId":
+			resp.MerchantId = value
+		case "payNo":
+			resp.PayNo = value
+		case "returnCode":
+			resp.ReturnCode = value
+		case "message":
+			resp.Message = value
+		case "signType":
+			resp.SignType = value
+		case "type":
+			resp.Type = value
+		case "version":
+			resp.Version = value
+		case "amount":
+			resp.Amount = value
+		case "orderId":
+			resp.OrderId = value
+		case "status":
+			resp.Status = value
+		case "serverCert":
+			resp.ServerCert = value
+		case "hmac":
+			resp.Hmac = value
+		}
+	}
+
+	return resp, nil
+}
+
+// verifyResponseSign 验证响应签名
+func (c *Client) verifyResponseSign(resp *RefundResponse) error {
+	// 构建参数字典
+	params := map[string]string{
+		"merchantId": resp.MerchantId,
+		"payNo":      resp.PayNo,
+		"returnCode": resp.ReturnCode,
+		"message":    resp.Message,
+		"signType":   resp.SignType,
+		"type":       resp.Type,
+		"version":    resp.Version,
+		"amount":     resp.Amount,
+		"orderId":    resp.OrderId,
+		"status":     resp.Status,
+	}
+
+	// 按文档指定顺序拼接签名串
+	signStr := buildSignString(params, getResponseSignKeys())
+
+	switch resp.SignType {
+	case SignTypeMD5:
+		if c.signKey == "" {
+			return ErrSignKeyEmpty
+		}
+		if !VerifyMD5(signStr, c.signKey, resp.Hmac) {
+			return ErrSignVerifyFailed
+		}
+		return nil
+	case SignTypeRSA:
+		if resp.ServerCert == "" {
+			return fmt.Errorf("response missing serverCert for RSA verification")
+		}
+		// 从证书中提取公钥
+		pubKeyPEM, err := extractPublicKeyFromCert(resp.ServerCert)
+		if err != nil {
+			return fmt.Errorf("extract public key from cert failed: %w", err)
+		}
+		return VerifyRSA(signStr, resp.Hmac, pubKeyPEM)
+	default:
+		return ErrSignTypeInvalid
+	}
+}
+
+// IsRefundSuccess 判断退款是否成功
+// 返回码为 000000 或 MCG00000 表示退款请求成功
+// 退款最终结果以 status 字段为准
+func IsRefundRequestSuccess(returnCode string) bool {
+	return returnCode == ReturnCodeSuccess || returnCode == ReturnCodeSuccessAlt
+}
+
+// IsRefundSuccess 判断退款最终结果是否成功
+func IsRefundSuccess(status string) bool {
+	return status == RefundStatusSuccess
+}
+```
+
+// File: hb/example_test.go
+```go
+package hb
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"testing"
+)
+
+// ExampleClient_Refund_MD5 使用MD5签名的退款示例
+func ExampleClient_Refund_MD5() {
+	// 创建客户端（使用MD5签名）
+	client, err := NewClient(
+		"888009941110054",
+		WithSignKey("your-64-digit-sign-key-here"),
+		WithBaseURL("https://uatipos.10086.cn"), // 测试环境
+	)
+	if err != nil {
+		log.Fatalf("创建客户端失败: %v", err)
+	}
+
+	// 构建退款请求
+	req := &RefundRequest{
+		RequestId: "20211105053044",
+		SignType:  SignTypeMD5,
+		OrderId:   "20211105045315",
+		Amount:    "1",
+	}
+
+	// 发送退款请求
+	resp, err := client.Refund(context.Background(), req)
+	if err != nil {
+		log.Fatalf("退款请求失败: %v", err)
+	}
+
+	fmt.Printf("返回码: %s\n", resp.ReturnCode)
+	fmt.Printf("退款结果: %s\n", resp.Status)
+	fmt.Printf("流水号: %s\n", resp.PayNo)
+
+	// 判断退款请求是否成功
+	if IsRefundRequestSuccess(resp.ReturnCode) {
+		fmt.Println("退款请求提交成功")
+	}
+
+	// 判断退款最终结果
+	if IsRefundSuccess(resp.Status) {
+		fmt.Println("退款最终成功")
+	}
+
+	// Output:
+	// 返回码: 000000
+	// 退款结果: SUCCESS
+	// 流水号: 205206151912517707
+	// 退款请求提交成功
+	// 退款最终成功
+}
+
+// ExampleClient_Refund_RSA 使用RSA签名的退款示例
+func ExampleClient_Refund_RSA() {
+	// 商户RSA私钥（PEM格式）
+	privateKey := `-----BEGIN PRIVATE KEY-----
+MIICdgIBADANBgkqhkiG9w0BAQEFAASCAmAwggJcAgEAAoGBAJ...（你的私钥）
+-----END PRIVATE KEY-----`
+
+	// 创建客户端（使用RSA签名）
+	client, err := NewClient(
+		"888009941110054",
+		WithPrivateKey(privateKey),
+		WithBaseURL("https://ipos.10086.cn"), // 生产环境
+	)
+	if err != nil {
+		log.Fatalf("创建客户端失败: %v", err)
+	}
+
+	// 构建退款请求
+	req := &RefundRequest{
+		RequestId: "20211105053044",
+		SignType:  SignTypeRSA,
+		OrderId:   "20211105045315",
+		Amount:    "1",
+	}
+
+	// 发送退款请求
+	resp, err := client.Refund(context.Background(), req)
+	if err != nil {
+		log.Fatalf("退款请求失败: %v", err)
+	}
+
+	fmt.Printf("返回码: %s\n", resp.ReturnCode)
+	fmt.Printf("退款结果: %s\n", resp.Status)
+
+	// Output:
+	// 返回码: 000000
+	// 退款结果: SUCCESS
+}
+
+// TestSignMD5 测试MD5签名
+func TestSignMD5(t *testing.T) {
+	signStr := "merchantId=888009941110054&requestId=20211105053044&signType=MD5&type=OrderRefund&version=2.0.0&orderId=20211105045315&amount=1"
+	signKey := "test-sign-key-64-chars-length-string-for-testing"
+
+	hmac := SignMD5(signStr, signKey)
+	if hmac == "" {
+		t.Error("MD5签名结果为空")
+	}
+	t.Logf("MD5签名结果: %s", hmac)
+
+	// 验证签名
+	if !VerifyMD5(signStr, signKey, hmac) {
+		t.Error("MD5签名验证失败")
+	}
+}
+
+// TestBuildSignString 测试签名串构建
+func TestBuildSignString(t *testing.T) {
+	params := map[string]string{
+		"merchantId": "888009941110054",
+		"requestId":  "20211105053044",
+		"signType":   "MD5",
+		"type":       "OrderRefund",
+		"version":    "2.0.0",
+		"orderId":    "20211105045315",
+		"amount":     "1",
+	}
+
+	keys := getRequestSignKeys()
+	signStr := buildSignString(params, keys)
+
+	expected := "merchantId=888009941110054&requestId=20211105053044&signType=MD5&type=OrderRefund&version=2.0.0&orderId=20211105045315&amount=1"
+	if signStr != expected {
+		t.Errorf("签名串不匹配\n期望: %s\n实际: %s", expected, signStr)
+	}
+}
+
+// TestParseResponse 测试响应解析
+func TestParseResponse(t *testing.T) {
+	rawResponse := `merchantId=888009941110054&payNo=205206151912517707&returnCode=000000&message=SUCCESS&signType=RSA&type=OrderRefund&version=2.0.0&amount=1&orderId=20211105045315&status=SUCCESS&serverCert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hmac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`
+
+	resp, err := parseResponse(rawResponse)
+	if err != nil {
+		t.Fatalf("解析响应失败: %v", err)
+	}
+
+	if resp.MerchantId != "888009941110054" {
+		t.Errorf("MerchantId不匹配: %s", resp.MerchantId)
+	}
+	if resp.PayNo != "205206151912517707" {
+		t.Errorf("PayNo不匹配: %s", resp.PayNo)
+	}
+	if resp.ReturnCode != "000000" {
+		t.Errorf("ReturnCode不匹配: %s", resp.ReturnCode)
+	}
+	if resp.Status != "SUCCESS" {
+		t.Errorf("Status不匹配: %s", resp.Status)
+	}
+	if resp.SignType != "RSA" {
+		t.Errorf("SignType不匹配: %s", resp.SignType)
+	}
+}
+
+// TestErrorCode 测试错误码映射
+func TestErrorCode(t *testing.T) {
+	tests := []struct {
+		code     string
+		expected string
+	}{
+		{"000000", "未知错误码"},
+		{"C01088", "退货金额域非法"},
+		{"D22201", "订单不存在"},
+		{"IPS0008", "签名不符，一般都是由于中文编码引起"},
+		{"UNKNOWN", "未知错误码"},
+	}
+
+	for _, tt := range tests {
+		desc := GetErrorDescription(tt.code)
+		if desc != tt.expected {
+			t.Errorf("错误码 %s: 期望 %s, 实际 %s", tt.code, tt.expected, desc)
+		}
+	}
+}
+
+// TestIsRefundSuccess 测试退款成功判断
+func TestIsRefundSuccess(t *testing.T) {
+	if !IsRefundRequestSuccess("000000") {
+		t.Error("000000 应该表示退款请求成功")
+	}
+	if !IsRefundRequestSuccess("MCG00000") {
+		t.Error("MCG00000 应该表示退款请求成功")
+	}
+	if IsRefundRequestSuccess("C01088") {
+		t.Error("C01088 不应该表示退款请求成功")
+	}
+
+	if !IsRefundSuccess("SUCCESS") {
+		t.Error("SUCCESS 应该表示退款最终成功")
+	}
+	if IsRefundSuccess("FAILED") {
+		t.Error("FAILED 不应该表示退款最终成功")
+	}
+}
+```
\ No newline at end of file