My colleague Albert van Veen wrote a blog post about Using ArgumentMatchers with Mockito. The idea is to let a mocked or stubbed service return a different value based on the argument passed into the service. This is inspired me to write the same sample with Spock.

Spock already has built-in mock and stub support, so first of all we don’t need an extra library to support mocking and stubbing. We can easily create a mock or stub with the Mock() and Stub() methods. We will see usage of both in the following examples.

In the first example we simply return true or false for ChocolateService.doesCustomerLikesChocolate() in the separate test methods.

import spock.lang.*

public class CandyServiceSpecification extends Specification {

    private ChocolateService chocolateService = Mock()
    private CandyService candyService = new CandyServiceImpl()
 
    def setup() {
        candyService.chocolateService = chocolateService
    }

    def "Customer Albert really likes chocolate"() {
        given:
        final Customer customer = new Customer(firstName: 'Albert')

        and: 'Mock returns true'
        1 * chocolateService.doesCustomerLikesChocolate(customer) >> true
        
        expect: 'Albert likes chocolate'
        candyService.getCandiesLikeByCustomer(customer).contains Candy.CHOCOLATE
    }

    def "Other customer do not like chocolate"() {
        given:
        final Customer customer = new Customer(firstName: 'Any other firstname')

        and: 'Mock returns false'
        1 * chocolateService.doesCustomerLikesChocolate(customer) >> false
        
        expect: 'Customer does not like chocolate'
        !candyService.getCandiesLikeByCustomer(customer).contains(Candy.CHOCOLATE)
    }

}

In the following example we mimic the ArgumentMatcher and this time we use a stub instead of mock.

import spock.lang.*

public class CandyServiceSpecification extends Specification {

    private CandyService candyService = new CandyServiceImpl()
 
    def setup() {
        candyService.chocolateService = Stub(ChocolateService) {
            getCandiesLikeByCustomer(_) >> { Customer customer ->
                customer?.firstName == 'Albert'
            }
        }
    }

    def "Customer Albert really likes chocolate"() {
        given:
        final Customer customer = new Customer(firstName: 'Albert')
        
        expect: 'Albert likes chocolate'
        candyService.getCandiesLikeByCustomer(customer).contains Candy.CHOCOLATE
    }

    def "Other customer do not like chocolate"() {
        given:
        final Customer customer = new Customer(firstName: 'Any other firstname')
        
        expect: 'Customer does not like chocolate'
        !candyService.getCandiesLikeByCustomer(customer).contains(Candy.CHOCOLATE)
    }

}

Code written with Spock 0.7-groovy-2.0