Test Screen allows you to check the behavior of the current screen. This will be done with the currently active model, toolset and graph set. It will also be done with the model in an idle mode (not in gaming or simulation setup). Because of this the current screen may behave differently than it would in the full Venapp. Usually, if you make sure you have the right model, graph set and toolset loaded you should get the same behavior. However, to put the Venapp into a gaming mode (which requires a Menu>Game command) you may need to open the Venapp on another screen that starts the gaming and, in the Venapp, switch to the screen with gaming controls.
When you click on the Test Screen button Vensim puts the Venapp into a special mode so that you can use Page Up and Page Down to pass through the screens, while the navigation buttons . You will also be given an option to suppress error messages that appear as you do this. What would normally appear as a message with an OK Button will be displayed
Click No to stop these messages from showing up.