Using Code Coverage
Code coverage shows you which of your app’s code paths are being tested. When you run a set of tests with code coverage enabled, Xcode tracks how many times each branch in your code is called. The test report shows a hierarchical view of test coverage for each file.
Clicking one of the files or methods opens an editor annotated with the number of times the unit tests call each code branch.
Turn on code coverage in the scheme editor for a target.
For more information on code coverage, see Code Coverage.