A method and system are provided for testing a graphical user (GUI) (204). The method includes applying a test step (208, 222) to a GUI under test (204) and finding a control in the GUI under test (204) to which the test step is to be applied. A model (210) is built dynamically of representations of the contents of the GUI under test (204) as a new control is found. The method includes finding a collection of dependent controls and representing the collection of controls in the GUI model (210) as a generalised pattern of the controls. The method applies a test step to the model (210) simultaneously with the GUI under test (204) and compares the results of the test step from the GUI under test (204) and from the model (210). If a test step is applied to the model and it is determined that a representation of the control to which the test step is to be applied is not provided in the model (210), a building rule (212) is executed to add a representation of the control to the model (210).