In Apache Wicket, so-called models are used to link the data and the representation in the graphical user interface. If models aren't used, one will never see the new value as during construction a fixed value is used. The GUI element will not look for a new value during a second rendering.
The situation can be corrected by passing a model to the used GUI element (e.g. ba passing the model to the GUI element's constructor).
Use automated UI Test, which is possible with the Selenium library and a browser driver. The browser driver allows us to run actions in a browser while writing code. The Selenium library is an interface to connect many browsers with the same code base. So now we are able to code a simple test, where a robot is automatically clicking through the website and trying out the login functionality. This technique may also apply to test other important and high priority UI features.