[hardwired]

Your only constructor

Code:

public GuiGuessingGameFrame(int mySecretNumber)

takes an int argument. In your test class you are using

Code:

new GuiGuessingGameApp();

a no–argument constructor which the class does not have.
If you do not explicitly define a constructor for a class java provides a no–argument constructor for it. If you provide any constructor that takes arguments you no longer get the default no–arg constructor from java. In this case you must add a no–argument constructor in the class.