Now, let's fix the error in the tests and learn how to run the previous test again. Open FirstDemoTests.swift, and run only the failing test by clicking on the diamond symbol next to the test method. The test still fails. Fix it by changing iS to Is in expectedOutput. Then, go to Product | Perform Action | Test "test_MakeHeadline_ReturnsStringWithEachWordStartCapital2()" Again, or use the shortcut ctrl + option + command + G to run just the previous test again. The shortcut is especially useful when you are working on one specific feature, and you need to test whether the implementation is already enough.