If your test suites are growing slower and you have already verified that it is not a serious problem with your application, first make your tests faster, then look at parallelization. The Test Load Balancer (TLB) project is a big development in the world of parallel test execution. It removes the inefficiencies of manual work distribution using smart algorithms and historical test execution data to optimize workload distribution and minimize elapsed time. Further, it orders the tests in intelligent ways like executing the test that failed in the previous execution first to get quicker feedback. Parallel execution can occur across a grid of machines or across multiple processes on a single machine. JUnit, RSpec, Test::Unit, Twist and Cucumber are currently supported and NUnit is under development.