How is 'automation testing' best defined?

Automation testing is best defined as utilizing tools to run tests automatically. This approach involves writing scripts or using automated testing frameworks to execute test cases without human intervention, allowing for repeated execution of tests in a consistent and efficient manner. Automation testing is particularly valuable for tasks that require extensive repetitive testing, such as regression tests, where the same tests need to be performed after each code change to ensure existing functionality remains intact.

The advantages of automation testing include increased test coverage, faster execution of tests, and the ability to run tests at any time without the need for manual effort. This capability helps teams to quickly identify defects and maintain the quality of their applications, especially in agile development environments where code changes frequently.

In contrast, the other options do not align with the definition of automation testing. Using spreadsheets to track tests focuses on organization and management rather than execution. Manual testing emphasizes human interaction in executing tests, which is the opposite of automation. Running tests only on the production environment is a risky strategy that does not encompass the full scope of testing practices, particularly in the context of automation where tests are frequently run in various environments.