Automation testing involves testing applications using tools rather than manually. There are various tools used by automation test engineers for different purposes, including test management, bug tracking, performance testing, and functional testing tools. The automation testing process involves test engineers writing test scripts based on test cases provided by manual testers. Automation testing is useful when there are multiple releases, regression test cycles, or repetitive tasks that need to be performed, as it saves time, allows faster execution by running tests in batches, and allows test scripts to be reused.