Mock Testing with Grails

For unit testing controllers that make calls to injected spring beans, we can use Grails' mock framework.

Take for example a Controller and Service class defined as follows

class MyService {
   boolean transactional = true

   def serviceMethod(param1) {
   return 'hi'
   }
}

class MyDomainController {
   def myService

   def doSomething = {
       def val = myService.serviceMethod('input1')
       return val    }
}

Our test case for the doSomething closure would look as follows

import grails.test.*

class MyDomainControllerTests extends ControllerUnitTestCase {

   protected void setUp() {
       super.setUp()
   }

   protected void tearDown() {
       super.tearDown()
   }

   void testSomething() {
       GrailsMock serviceMock = mockFor(MyService)

       /*
        * Mock the method being called
        * the 1..1 specifies the min & max number of times the method is expected to be called
        * the closure defines the code executed each time the method is called
        */
       serviceMock.demand.serviceMethod(1..1) {param1 ->
           assertEquals 'input1', param1
           return 'hi'
       }

       /*
        * The service needs to be manually set in the controller
        */ 
       controller.myService = serviceMock.createMock()
      
       assertEquals 'hi', controller.doSomething()

       /*
        * Verifies that the service was accessed
        * in the manner established earlier.
        */
       serviceMock.verify()
   }
}