When we use $ grails test-app to test our code all tests are run. We can specify a single test class as an argument for the test-app script. So for example if we have a HelloWorldControllerTests class we use the following command $ grails test-app HelloWorldController. Grails supports wildcards for defining the test class, so we can also use $ grails test-app Hello* for example.
But we can even specify the method in our HelloWorldControllerTests class we want to be tested. If the test class has the method testSayHello() we use the following command $ grails test-app HelloWorldController.sayHello and only the testSayHello().
