Be your own QA engineer

When you think you are done with a feature (such as a component), you probably aren't 😄. Test your feature on different screen sizes and on different devices, either physically or by using BrowserStack.

Use the component/feature/page from the perspective of end user. Try to notice if things like visible hover and focus states are missing. Write accessible code. Try to use keyboard on your site and see if it's possible to navigate through it.

Despite the fact we might have a QA engineer on the project to test the software, it should be the goal of the development group that QA finds nothing wrong.