The purpose of testing is to discover errors. Testing is the process of trying to discover every conceivable fault or weakness in a work product.

• Beta testing: Operational testing at a site not otherwise involved with the software developers.
• Stress testing: Testing conducted to evaluate a system or component at or beyond the limits of its specified requirements.
• Regression testing: Rerunning test cases which a program has previously executed correctly in order to detect errors spawned by changes or corrections made during software development and maintenance  
• Alpha testing: Testing of a software product or system conducted at the developer's site by the customer
• Compliance testing:  Conformance testing or type testing is testing to determine whether a system meets some specified standard.
• Acceptance testing: Testing conducted to enable a user/customer to determine whether to accept a software product. Normally performed to validate the software meets a set of agreed acceptance criteria.