Change In MetaClass Behavior

package demo

class Widget {

    static Integer someNumber = 42
}

package demo

class WidgetSpec extends spock.lang.Specification {

    void 'test property access'() {
        given:
        Widget.metaClass.getSomeNumber = {
            2112
        }

        when:
        def widget = new Widget()

        then:
        widget.someNumber == 2112
    }
}