1. An apparatus for application testing, comprising: a data repository configured to store a copy of some or all of a set of stored reference data; and a test data generation component configured to generate a set of input data for testing an application that processes a set of received input data and the set of stored reference data according to a data processing operation, the set of received input data and set of stored reference data each comprising one or more attributes, the one or more attributes each having at least one value, wherein the test data generation component is configured to generate the set of input data by: selecting at least one value from the copy of the set of stored reference data, and outputting the selected at least one value in the generated set of input data for testing the application.