A pneumatic test plug for clean-out tees and a method of testing a pipeline are disclosed. The pneumatic test plug includes a cap and a bladder. The cap has an inflation inlet and a testing fluid inlet. The testing fluid inlet provides a conduit for a testing fluid. The testing fluid may be a liquid or a gas. The bladder is in fluid connection with the inflation inlet. The bladder has an open end and a closed end. The open end receives air from the inflation inlet. The closed end is opposite the open end. The testing fluid inlet provides testing fluid through the cap and outside of the bladder. The inflation inlet provides a passageway to the bladder.