add more tests

ChatBot/Services/SystemPromptService.cs

@@ -78,7 +78,7 @@ namespace ChatBot.Services
             await GetSystemPromptAsync();
         }
 
-        private const string DefaultPrompt =
+        public const string DefaultPrompt =
             "You are a helpful AI assistant. Provide clear, accurate, and helpful responses to user questions.";
     }
 }