public void validateDocumentGraph(List<SDDocumentType> documents) {
        for (SDDocumentType document : documents) {
            validateRoot(document);
        }
    }
@Test
    void simple_ref_dag_is_allowed() {
        Schema advertiserSchema = createSearchWithName("advertiser");
        Schema campaignSchema = createSearchWithName("campaign");
        Schema adSchema = createSearchWithName("ad");
        createDocumentReference(adSchema, advertiserSchema, "advertiser_ref");
        createDocumentReference(adSchema, campaignSchema, "campaign_ref");

        DocumentGraphValidator validator = new DocumentGraphValidator();
        validator.validateDocumentGraph(documentListOf(advertiserSchema, campaignSchema, adSchema));
    }