A system and method are provided for testing the performance of applications. By way of example only, the method may include training a neural network with documents containing text elements that are arranged in accordance with a defined format and using the neural network to determine the predictability of the value of individual text elements within a test document. When the neural network indicates that the value of a text element is unlikely, the value may be modified and the modified document may be used to test an application that processes documents in accordance with the defined format.