My whole life I have written unit tests to check my functionality/any bugs. How is software like Jenkins able to build and test thousands of lines of code? Who even writes those tests? If they’re writing all those tests, why not test locally? What is the purpose of automation?
Exactly that. Automation. Sure you can run a unit test yourself. Can you run it across different environments? How about concurrently? How about every single time you check in your code? How about in the middle of the night for a nightly build?