make sure to close off all the channels at the end

test/src/main/java/org/jvnet/hudson/test/HudsonTestCase.java

@@ -72,6 +72,8 @@ import hudson.model.TaskListener;
 import hudson.model.UpdateSite;
 import hudson.model.User;
 import hudson.model.View;
+import hudson.remoting.Channel;
+import hudson.remoting.VirtualChannel;
 import hudson.remoting.Which;
 import hudson.security.ACL;
 import hudson.security.AbstractPasswordBasedSecurityRealm;
@@ -233,6 +235,11 @@ public abstract class HudsonTestCase extends TestCase implements RootAction {
      */
     private List<WebClient> clients = new ArrayList<WebClient>();
 
+    /**
+     * Remember channels that are created, to release them at the end.
+     */
+    private List<Channel> channels = new ArrayList<Channel>();
+
     /**
      * JavaScript "debugger" that provides you information about the JavaScript call stack
      * and the current values of the local variables in those stack frame.
@@ -344,6 +351,13 @@ public abstract class HudsonTestCase extends TestCase implements RootAction {
                 client.closeAllWindows();
             }
             clients.clear();
+
+            for (Channel c : channels)
+                c.close();
+            for (Channel c : channels)
+                c.join();
+            channels.clear();
+
         } finally {
             server.stop();
             for (LenientRunnable r : tearDowns)
@@ -433,6 +447,17 @@ public abstract class HudsonTestCase extends TestCase implements RootAction {
         return realm;
     }
 
+    @TestExtension
+    public static class ComputerListenerImpl extends ComputerListener {
+        @Override
+        public void onOnline(Computer c, TaskListener listener) throws IOException, InterruptedException {
+            VirtualChannel ch = c.getChannel();
+            if (ch instanceof Channel)
+            TestEnvironment.get().testCase.channels.add((Channel)ch);
+        }
+    }
+
+
 //    /**
 //     * Sets guest credentials to access java.net Subversion repo.
 //     */