1 * writeIndex.lookup("key") >> null
        1 * readIndex.lookup("key")

        when:
        twoStageIndex.lookup("other")

        then:
        1 * writeIndex.lookup("other") >> Stub(CachedExternalResource)
        0 * readIndex._
    }

    def "clearing delegates to the writable cache"() {
        when:
        twoStageIndex.clear("key")

        then:
        1 * writeIndex.clear("key")