private static ContentCluster createClusterWithThreeDocumentTypes() throws Exception {
        List<String> schemas = new ArrayList<>();
        schemas.add(new SchemaBuilder().name("a")
                                       .content(joinLines("field ref_to_b type reference<b> { indexing: attribute }",
                                                          "field ref_to_c type reference<c> { indexing: attribute }"))
                                       .build());
        schemas.add(new SchemaBuilder().name("b")
                                       .content("field ref_to_c type reference<c> { indexing: attribute }")
                                       .build());
        schemas.add(new SchemaBuilder().name("c").build());
        return createCluster(new ContentClusterBuilder().docTypes(List.of(DocType.index("a"),
                                                                          DocType.indexGlobal("b"),
                                                                          DocType.indexGlobal("c"))).getXml(),
                             schemas);
    }
Unit tests for content search cluster.

@author geirst
config-model/src/test/java/com/yahoo/vespa/model/content/ContentSchemaClusterTest.java