refactoring

EpsonPrintService/HeartbeatBackgroundTask.cs

@@ -17,11 +17,12 @@ public class HeartbeatBackgroundTask
 
     public HeartbeatBackgroundTask(
         EpsonPrintServiceConfiguration configuration,
-        ILogger logger)
+        ILogger logger,
+        HttpClient httpClient)
     {
         _configuration = configuration;
         _logger = logger;
-        _httpClient = new HttpClient();
+        _httpClient = httpClient;
         _interval = TimeSpan.FromSeconds(30);
     }