If you’re a developer, then you have already performed a software test, whether you realize it or not. When you write a piece of software, to see if it's working, that's testing.
When you create a webform, then submit the form to see if it successfully adds the data to the database; that’s testing. When you submit the same form again, with the wrong input, to see if it rejects the form and tells the user there’s a problem, that’s also testing but manual testing.
Read more: https://www.microverse.org/blog/test-driven-development-with-rspec-in-ruby-on-rails