What does the term 'test levels' refer to in software testing?

The term 'test levels' in software testing refers to the various stages of testing that occur during the software development process. These levels describe the different phases through which software passes from the development stage until it is released. Common levels of testing include unit testing, integration testing, system testing, and acceptance testing. Each level targets a specific aspect of the software—unit testing focuses on individual components, integration testing checks interactions between components, system testing evaluates the complete system as a whole, and acceptance testing ensures the software meets the requirements from a user perspective.

Understanding these levels helps testers structure their testing efforts, ensuring that all necessary areas are adequately assessed throughout the development cycle. It also allows teams to identify which tests should be performed at each stage, facilitating a systematic approach to quality assurance.