What is the smallest unit of testing when performing unit testing?

The smallest unit of testing in the context of unit testing is a test case. This is because a test case is a specific set of conditions or variables under which a tester determines whether a system or software application is functioning correctly. It typically includes inputs, execution conditions, and expected results—to verify that a particular feature or functionality of the software works as intended.

By focusing on individual components or functions, a test case isolates a piece of code to validate its correctness. This level of granularity allows for effective identification of bugs or issues in the codebase, making unit testing an essential practice for ensuring software reliability.

Other terms such as test fixture, test runner, and test collector refer to supportive elements in the testing process rather than units of testing themselves. A test fixture sets up the environment for tests, ensuring that they are executed in a consistent state. A test runner manages the execution of tests and reports their results, while a test collector gathers multiple test cases for execution. Although these components are important to the testing framework, they do not serve as the smallest unit being tested.