Added FormValidation for testing connection to Flowdock.

src/main/java/com/flowdock/jenkins/FlowdockNotifier.java

@@ -18,6 +18,9 @@
 
 import javax.servlet.ServletException;
 import java.io.IOException;
+import java.io.PrintStream;
+import java.io.StringWriter;
+import java.io.ByteArrayOutputStream;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -112,6 +115,23 @@ public String getDisplayName() {
             return "Flowdock notification";
         }
 
+        public FormValidation doTestConnection(@QueryParameter("flowToken") final String flowToken,
+            @QueryParameter("notificationTags") final String notificationTags) {
+            ByteArrayOutputStream baos = new ByteArrayOutputStream();
+            PrintStream ps = new PrintStream(baos);
+
+            FlowdockAPI api = new FlowdockAPI(apiUrl(), flowToken, ps);
+            ChatMessage testMsg = new ChatMessage();
+            testMsg.setTags(notificationTags);
+            testMsg.setContent("Your plugin is ready!");
+
+            if(api.pushChatMessage(testMsg)) {
+                return FormValidation.ok("Success! Flowdock plugin can send notifications to your flow.");
+            } else {
+                return FormValidation.error(baos.toString());
+            }
+        }
+
         @Override
         public boolean configure(StaplerRequest req, JSONObject formData) throws FormException {
             apiUrl = formData.getString("apiUrl");

src/main/resources/com/flowdock/jenkins/FlowdockNotifier/config.jelly

@@ -8,6 +8,10 @@
     <f:textbox />
   </f:entry>
 
+  <f:validateButton
+     title="Test connection with Chat notification" progress="Sending..."
+     method="testConnection" with="flowToken,notificationTags" />
+
   <f:entry title="Chat notification when build fails" field="chatNotification">
     <f:checkbox />
   </f:entry>