In general, software testing is a process of evaluating a product to verify that product meets its requirements and other basic industrial requirements. How it is different from open source testing? In open source project, testing is an information gathering service. Testers gather information about product by exploring it, questioning it, learning from the product and from past experiences. Open source projects bring real flavor to testing. Testing have many dimensional; capturing all dimensions in a formal process and documenting them in any kind of projects is highly impossible. This talk will cover key things in mastering the art of open source testing; that includes effective open source testing, how effective testing can revitalize open source testing, mission of testing, mind-mapping testing ideas, impossibility of complete testing, mistakes most volunteers make in open source testing and finally challenging testing tasks for attendees.