Hybrid monkey testing: enhancing automated GUI tests with random test generation

Many software projects maintain automated GUI tests that are repeatedly executed for regression testing. Every test run executes exactly the same fixed sequence of steps confirming that the currently tested version shows precisely the same behavior as the last version. The confirmatory approach implemented by these tests limits their ability to find new defects. We therefore propose to combine existing automated regression tests with random test generation. Random test generation creates a rich variety of test steps that interact with the system under test in new, unexpected ways. Enhancing existing test cases with random test steps allows revealing new, hidden defects with little extra effort. In this paper we describe our implementation of a hybrid approach that enhances existing GUI test cases with additional, randomly generated interactions. We conducted an experiment using a mature, widely-used open source application. On average the added random interactions increased the number of visited application windows per test by 23.6% and code coverage by 12.9%. Running the enhanced tests revealed three new defects.