What is a test case in software testing?

A test case is a documented set of steps, inputs, and expected results used to verify one behavior. It usually includes preconditions (user role, data state), actions, and pass/fail criteria so different testers get consistent outcomes. Test cases live in test management tools, spreadsheets, or specs linked to requirements. They differ from test scripts: a case describes what to verify; automation implements how to run it repeatedly. Well-written cases are atomic - one main assertion per case - so failures pinpoint defects. Suites of cases map to user stories, risks, or compliance requirements. Maintaining cases as the product changes is ongoing QA work, not a one-time documentation task.