MM-18881 - Attempting to configure uninstalled plugins gets st… (#12687)

* MM-18881 - Attempting to configure uninstalled plugins gets stuck at Loading... without timeout.

* Added a test

* Closing websocketclient

api4/plugin_test.go

@@ -305,11 +305,34 @@ func TestNotifyClusterPluginEvent(t *testing.T) {
 	require.Equal(t, "testplugin", manifest.Id)
 
 	// Successful remove
+	webSocketClient, err := th.CreateWebSocketSystemAdminClient()
+	require.Nil(t, err)
+	webSocketClient.Listen()
+	defer webSocketClient.Close()
+	done := make(chan bool)
+	go func() {
+		for {
+			select {
+			case resp := <-webSocketClient.EventChannel:
+				if resp.Event == model.WEBSOCKET_EVENT_PLUGIN_STATUSES_CHANGED && len(resp.Data["plugin_statuses"].([]interface{})) == 0 {
+					done <- true
+					return
+				}
+			case <-time.After(5 * time.Second):
+				done <- false
+				return
+			}
+		}
+	}()
+
 	testCluster.ClearMessages()
 	ok, resp := th.SystemAdminClient.RemovePlugin(manifest.Id)
 	CheckNoError(t, resp)
 	require.True(t, ok)
 
+	result := <-done
+	require.True(t, result, "plugin_statuses_changed websocket event was not received")
+
 	messages = testCluster.GetMessages()
 
 	expectedRemoveMessage := &model.ClusterMessage{