}
        ''')

        when:
        extractor.extract(source)

        then:
        extractor.cache.size() == 1

        when:
        cl.clearCache()
        forcefullyClearReferences(source)
        source = null

        then:
        ConcurrentTestUtil.poll(10) {
            System.gc()
            extractor.cache.cleanUp()
            extractor.cache.size() == 0
        }