In this paper, we present a high-level functional test methodology for Gals systems. In this new test methodology, the self-timed wrapper of a Gals module is enhanced by a test extension element that provides a unified interface to a centralized test controller. Each test extension element is customized for the locally-synchronous island it is attached to, and is able to decouple the asynchronous communication ports from the locally-synchronous islands in a test mode. The test controller can then issue a series of commands to the test extension elements to initiate data transfers between Gals modules. Testing is achieved by observing these data transfers through the test extension elements. We also introduce a simple design automation solution to customize both the test extension element and the test controller for the Gals system.