New: App health displayed in UI

src/NzbDrone.Core/HealthCheck/Checks/DownloadClientCheck.cs

@@ -0,0 +1,36 @@
+using System;
+using NzbDrone.Core.Download;
+
+namespace NzbDrone.Core.HealthCheck.Checks
+{
+    public class DownloadClientCheck : IProvideHealthCheck
+    {
+        private readonly IProvideDownloadClient _downloadClientProvider;
+
+        public DownloadClientCheck(IProvideDownloadClient downloadClientProvider)
+        {
+            _downloadClientProvider = downloadClientProvider;
+        }
+
+        public HealthCheck Check()
+        {
+            var downloadClient = _downloadClientProvider.GetDownloadClient();
+
+            if (downloadClient == null)
+            {
+                return new HealthCheck(HealthCheckResultType.Warning, "No download client is available");
+            }
+
+            try
+            {
+                downloadClient.GetQueue();
+            }
+            catch (Exception)
+            {
+                return new HealthCheck(HealthCheckResultType.Error, "Unable to communicate with download client");
+            }
+
+            return null;
+        }
+    }
+}