Refactor ToUserAgentHeaderString and add new test

Refactored the ToUserAgentHeaderString method in Marshaller.cs to use a switch statement instead of if-else statements, including a default case for converting requestRetryMode to lowercase. Removed Debug.Assert for retryMode and directly appended it to the StringBuilder object. Added LookForRequestRetryModeChanges test in StaticCheckTests.cs to verify the integrity of the RequestRetryMode enum.

sdk/src/Core/Amazon.Runtime/Pipeline/Handlers/Marshaller.cs

@@ -115,9 +115,7 @@ private static void SetUserAgentHeader(IRequestContext requestContext)
             if (!string.IsNullOrEmpty(clientAppId))
                 sb.Append(" app/").Append(InternalSDKUtils.ReplaceInvalidUserAgentCharacters(clientAppId));
 
-            var retryMode = ToUserAgentHeaderString(requestContext.ClientConfig.RetryMode);
-            Debug.Assert(retryMode != requestContext.ClientConfig.RetryMode.ToString().ToLower(), "Invalid RetryMode string.");
-            sb.Append(" cfg/retry-mode#}").Append(retryMode);
+            sb.Append(" cfg/retry-mode#}").Append(ToUserAgentHeaderString(requestContext.ClientConfig.RetryMode));
 
             sb.Append(" md/").Append(requestContext.IsAsync ? "ClientAsync" : "ClientSync");
 
@@ -143,10 +141,15 @@ private static void SetUserAgentHeader(IRequestContext requestContext)
 
         private static string ToUserAgentHeaderString(RequestRetryMode requestRetryMode)
         {
-            if (requestRetryMode == RequestRetryMode.Adaptive)
-                return "adaptive";
-            else
-                return "standard";
+            switch (requestRetryMode)
+            {
+                case RequestRetryMode.Standard:
+                    return "standard";
+                case RequestRetryMode.Adaptive:
+                    return "adaptive";
+                default:
+                    return requestRetryMode.ToString().ToLowerInvariant();
+            }
         }
     }
 }

sdk/test/Services/SecurityToken/UnitTests/Custom/StaticCheckTests.cs

@@ -83,5 +83,15 @@ public void EnsureCredentialProfileDetectorSetup()
             // the properties are used at least once.
             Assert.IsTrue(profileOptionsProperties.SetEquals(referencedProfileOptionsProperties));
         }
+
+        [TestMethod]
+        public void LookForRequestRetryModeChanges()
+        {
+            var expectedHash = "2FC699DB6A4284C5D53F3B7FA4E64165576FD1F6AE458BC737AE503F06DFBE4C";
+            AssertExtensions.AssertEnumUnchanged(
+                typeof(RequestRetryMode),
+                expectedHash,
+                "The Amazon.Runtime.Internal.Marshaller.ToUserAgentHeaderString method implementation may need to be updated.");
+        }
     }
 }