From their description on github:
The Rootbeer GPU Compiler makes it easy to use Graphics Processing Units from within Java.
And it has been developed in TDD style:
Rootbeer was created using Test Driven Development and testing is essentially important in Rootbeer. Rootbeer is 20k lines of product for and 7k of test code and all tests pass on both Windows and Linux. The Rootbeer test case suite covers every aspect of the Java Programming language except:
1. native methods
3. dynamic method invocation
4. sleeping while inside a monitor.