Answer: Unit testing

### Explanation **Unit testing** is the practice of testing small, isolated, and self-contained pieces of code, such as a single function or method. Databricks defines unit testing as an approach to testing self-contained units of code early and often. Verifying the logic of a specific mathematical routine in isolation is a classic example of a unit test. ### Why the other options are incorrect: * **Manual testing** involves human execution and observation without automated assertions; the scenario describes a line of code (automated). * **Functional testing** validates an application's behavior against user-facing requirements, typically involving multiple units working together. * **Integration testing** focuses on the interaction between different components or systems (e.g., how a function interacts with a database), rather than a numeric routine in isolation. * **End-to-end testing** validates the entire data pipeline or application workflow from input to output, which is much broader than testing a single algorithm.

Author: LeetQuiz Editorial Team