diff --git a/src/v4/aliyun_util.rs b/src/v4/aliyun_util.rs
index 4bce013..f399d61 100644
--- a/src/v4/aliyun_util.rs
+++ b/src/v4/aliyun_util.rs
@@ -156,6 +156,7 @@ fn get_signature(sign_algorithm: &SignAlgorithm,
     string_to_sign.push_str(payload);
 
     let string_to_sign_digest_hex = sign_algorithm.digest(string_to_sign.as_bytes());
+    let mut string_to_sign = String::new();
     string_to_sign.push_str(sign_algorithm.as_aliyun_name_v4());
     string_to_sign.push('\n');
     string_to_sign.push_str(&string_to_sign_digest_hex);
@@ -219,3 +220,147 @@ fn get_signed_headers(headers: &BTreeMap<String, String>) -> Vec<(String, &Strin
     }
     signed_headers
 }
+
+#[test]
+fn test_get_nonce() {
+    let nonce = get_nonce();
+    assert!(nonce.starts_with("nonce-"));
+}
+
+#[test]
+fn test_get_signing_key_sha256() {
+    let signing_key = get_signing_key(
+        &SignAlgorithm::Sha256,
+        "AccessKeySecret",
+        "20121231",
+        "cn-hangzhou",
+        "test");
+    assert_eq!(
+        "7a297f88537fed9e2e2ad740cd945860ce62df50c425e4a73f6414c0aa1cd04a",
+        hex::encode(&signing_key)
+    );
+}
+
+#[test]
+fn test_get_signing_key_sm3() {
+    let signing_key = get_signing_key(
+        &SignAlgorithm::Sm3,
+        "AccessKeySecret",
+        "20121231",
+        "cn-hangzhou",
+        "test");
+    assert_eq!(
+        "a54b85a3b1e6a04c939cf807c1d6bc131877527122b2d2dfc5df94b86b8d8a83",
+        hex::encode(&signing_key)
+    );
+}
+
+#[test]
+fn test_get_signed_headers_01() {
+    let mut headers = BTreeMap::new();
+    headers.insert("host".to_string(), "example.com".to_string());
+    let signed_headers = get_signed_headers(&headers);
+    let signed_headers = signed_headers.iter().map(|h| &h.0).collect::<Vec<_>>();
+
+    assert_eq!(1, signed_headers.len());
+    assert_eq!("host", signed_headers[0].as_str());
+}
+
+#[test]
+fn test_get_signed_headers_02() {
+    let mut headers = BTreeMap::new();
+    headers.insert("host".to_string(), "example.com".to_string());
+    headers.insert("x-acs-date".to_string(), "19700112T010101Z".to_string());
+    let signed_headers = get_signed_headers(&headers);
+    let signed_headers = signed_headers.iter().map(|h| &h.0).collect::<Vec<_>>();
+
+    assert_eq!(2, signed_headers.len());
+    assert_eq!("host", signed_headers[0].as_str());
+    assert_eq!("x-acs-date", signed_headers[1].as_str());
+}
+
+#[test]
+fn test_get_signed_headers_03() {
+    let mut headers = BTreeMap::new();
+    headers.insert("host".to_string(), "example.com".to_string());
+    headers.insert("x-acs-date".to_string(), "19700112T010101Z".to_string());
+    headers.insert("content-type".to_string(), "application/json".to_string());
+    let signed_headers = get_signed_headers(&headers);
+    let signed_headers = signed_headers.iter().map(|h| &h.0).collect::<Vec<_>>();
+
+    assert_eq!(3, signed_headers.len());
+    assert_eq!("content-type", signed_headers[0].as_str());
+    assert_eq!("host", signed_headers[1].as_str());
+    assert_eq!("x-acs-date", signed_headers[2].as_str());
+}
+
+#[test]
+fn test_build_canonicalized_headers_01() {
+    let mut headers = BTreeMap::new();
+    headers.insert("host".to_string(), "example.com".to_string());
+    headers.insert("x-acs-date".to_string(), "19700112T010101Z".to_string());
+    headers.insert("content-type".to_string(), "application/json".to_string());
+
+    let canonicalized_headers = build_canonicalized_headers(&headers);
+    assert_eq!(r#"content-type:application/json
+host:example.com
+x-acs-date:19700112T010101Z
+"#, canonicalized_headers.as_str());
+}
+
+#[test]
+fn test_build_canonicalized_headers_02() {
+    let mut headers = BTreeMap::new();
+    headers.insert("host".to_string(), "example.com".to_string());
+    headers.insert("x-acs-date".to_string(), "19700112T010101Z".to_string());
+    headers.insert("content-type".to_string(), "application/json!@#$%^&*()_+[]{};':\"".to_string());
+
+    let canonicalized_headers = build_canonicalized_headers(&headers);
+    assert_eq!(r#"content-type:application/json!@#$%^&*()_+[]{};':"
+host:example.com
+x-acs-date:19700112T010101Z
+"#, canonicalized_headers.as_str());
+}
+
+#[test]
+fn test_build_canonicalized_resource() {
+    let mut query = BTreeMap::new();
+    query.insert("host".to_string(), "example.com".to_string());
+    query.insert("x-acs-date".to_string(), "19700112T010101Z".to_string());
+    query.insert("content-type".to_string(), "application/json!@#$%^&*()_+[]{};':\"".to_string());
+
+    let canonicalized_query = build_canonicalized_resource(&query);
+    assert_eq!("content-type=application%2Fjson%21%40%23%24%25%5E%26%2A%28%29_%2B\
+    %5B%5D%7B%7D%3B%27%3A%22&host=example.com&x-acs-date=19700112T010101Z", canonicalized_query.as_str());
+}
+
+#[test]
+fn test_get_region() {
+    assert_eq!("center", get_region("", ""));
+    assert_eq!("cn-hangzhou", get_region("ecs", "ecs.cn-hangzhou.aliyuncs.com"));
+    assert_eq!("center", get_region("ecs", "ecs.aliyuncs.com"));
+}
+
+#[test]
+fn test_get_signature() {
+    let signing_key = get_signing_key(
+        &SignAlgorithm::Sha256,
+        "AccessKeySecret",
+        "20121231",
+        "cn-hangzhou",
+        "test");
+
+    let query = BTreeMap::new();
+    let mut headers = BTreeMap::new();
+    headers.insert("host".to_string(), "example.com".to_string());
+    let sig = get_signature(
+        &SignAlgorithm::Sha256,
+        &signing_key,
+        "/test",
+        "POST",
+        &query,
+        &headers,
+        "PAYLOAD",
+    );
+    assert_eq!("ee5033e71c4674a94c511ac177f2a2f41835d2c8724f8a98632a2193786ce40b", sig.as_str());
+}
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