improve UserAgent for csharp

.gitignore

@@ -23,3 +23,4 @@ java/.classpath
 cc/*.o
 python/**/__pycache__/
 cache/
+csharp/tests/coverage.xml

csharp/core/Common.cs

@@ -182,7 +182,7 @@ public static string ToFormString(Dictionary<string, object> map)
             return result.ToString();
         }
 
-        public static string ToJSONString(Object value)
+        public static string ToJSONString(object value)
         {
             if (value is string)
             {
@@ -458,15 +458,10 @@ public static Stream AssertAsReadable(object a)
 
         internal static string GetDefaultUserAgent()
         {
-            string defaultUserAgent = string.Empty;
             string OSVersion = Environment.OSVersion.ToString();
             string ClientVersion = GetRuntimeRegexValue(RuntimeEnvironment.GetRuntimeDirectory());
             string CoreVersion = Assembly.GetExecutingAssembly().GetName().Version.ToString();
-            defaultUserAgent = "Alibaba Cloud (" + OSVersion + ") ";
-            defaultUserAgent += ClientVersion;
-            defaultUserAgent += " Core/" + CoreVersion;
-            defaultUserAgent += " TeaDSL/1";
-            return defaultUserAgent;
+            return string.Format("AlibabaCloud ({0}) {1} Core/{2} TeaDSL/1", OSVersion, ClientVersion, CoreVersion);
         }
 
         internal static string GetRuntimeRegexValue(string value)

csharp/tests/CommonTest.cs

@@ -317,6 +317,10 @@ public void Test_GetUserAgent()
         {
             Assert.NotNull(Common.GetUserAgent(null));
 
+            string ua = Common.GetUserAgent("").Trim();
+            Assert.StartsWith("AlibabaCloud (", ua);
+            Assert.EndsWith("TeaDSL/1", ua);
+
             Assert.Contains("test", Common.GetUserAgent("test"));
         }