Cassandra Unit Testing with Byteman

The Apache Cassandra project has recently begun exploring Byteman, an open-source tool that enables additional Java code to be injected into a running JVM. This tool can increase observability and facilitate fault injection testing in unit tests by injecting code at specific points in the existing code. Byteman is useful for verifying behaviors without easily observable side effects and simulating pathological conditions, such as disk filling up or network partitioning. The tool has been integrated with JUnit test runner to support integration with test fixtures through annotations. In a recent Cassandra unit test, Byteman was used to assert that the HintsBufferPool provides backpressure to its callers by drawing write buffers from a BlockingQueue.