groovy mocks are not truthy

Originally reported on Google Code with ID 316

See the example below.
Regular mocks evaluate to true but groovy mocks resolve to false.

class GroovyMockSpec extends Specification {
    def mock = Mock(A)
    def groovyMock = GroovyMock(Object)

    def "regular mocks are truthy"() {
        expect:
        mock ?: 'irrelevant' == mock
    }

    def "groovy mocks are falsey"() {
        expect:
        groovyMock ?: 'unexpected' == 'unexpected'
    }

    static interface A {}
}

What version of Spock and Groovy are you using?
0.7-groovy-1.8

Reported by sgo@thinkerit.be on 2013-06-17 12:36:31

Start by reproducing the provided GroovyMockSpec example with Spock 0.7-groovy-1.8 and compare the truthiness of regular and Groovy mocks. Trace the existing mock behavior to determine the intended change; done means Groovy mocks evaluate truthily like regular mocks without breaking the example's expectations.