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diff --git a/config-model/src/test/java/com/yahoo/schema/DocumentGraphValidatorTest.java b/config-model/src/test/java/com/yahoo/schema/DocumentGraphValidatorTest.java
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+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.schema;
+
+import com.yahoo.config.model.test.MockApplicationPackage;
+import com.yahoo.documentmodel.NewDocumentReferenceDataType;
+import com.yahoo.schema.document.SDDocumentType;
+import com.yahoo.schema.document.SDField;
+import com.yahoo.schema.document.TemporarySDField;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static java.util.stream.Collectors.toList;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+/**
+ * @author bjorncs
+ */
+public class DocumentGraphValidatorTest {
+
+    @SuppressWarnings("deprecation")
+    @Rule
+    public final ExpectedException exceptionRule = ExpectedException.none();
+
+    @Test
+    public 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));
+    }
+
+    @Test
+    public void simple_inheritance_dag_is_allowed() {
+        Schema grandfather = createSearchWithName("grandfather");
+        Schema father = createSearchWithName("father", grandfather);
+        Schema son = createSearchWithName("son", father);
+
+        DocumentGraphValidator validator = new DocumentGraphValidator();
+        validator.validateDocumentGraph(documentListOf(son, father, grandfather));
+    }
+
+    @Test
+    public void complex_dag_is_allowed() {
+        Schema grandfather = createSearchWithName("grandfather");
+        Schema father = createSearchWithName("father", grandfather);
+        Schema mother = createSearchWithName("mother", grandfather);
+        createDocumentReference(father, mother, "wife_ref");
+        Schema son = createSearchWithName("son", father, mother);
+        Schema daughter = createSearchWithName("daughter", father, mother);
+        createDocumentReference(daughter, son, "brother_ref");
+
+        Schema randomGuy1 = createSearchWithName("randomguy1");
+        Schema randomGuy2 = createSearchWithName("randomguy2");
+        createDocumentReference(randomGuy1, mother, "secret_ref");
+
+        DocumentGraphValidator validator = new DocumentGraphValidator();
+        validator.validateDocumentGraph(documentListOf(son, father, grandfather, son, daughter, randomGuy1, randomGuy2));
+    }
+
+    @Test
+    public void ref_cycle_is_forbidden() {
+        Schema schema1 = createSearchWithName("doc1");
+        Schema schema2 = createSearchWithName("doc2");
+        Schema schema3 = createSearchWithName("doc3");
+        createDocumentReference(schema1, schema2, "ref_2");
+        createDocumentReference(schema2, schema3, "ref_3");
+        createDocumentReference(schema3, schema1, "ref_1");
+
+        DocumentGraphValidator validator = new DocumentGraphValidator();
+        exceptionRule.expect(DocumentGraphValidator.DocumentGraphException.class);
+        exceptionRule.expectMessage("Document dependency cycle detected: doc1->doc2->doc3->doc1.");
+        validator.validateDocumentGraph(documentListOf(schema1, schema2, schema3));
+    }
+
+    @Test
+    public void inherit_cycle_is_forbidden() {
+        Schema schema1 = createSearchWithName("doc1");
+        Schema schema2 = createSearchWithName("doc2", schema1);
+        Schema schema3 = createSearchWithName("doc3", schema2);
+        schema1.getDocument().inherit(schema3.getDocument());
+
+        DocumentGraphValidator validator = new DocumentGraphValidator();
+        exceptionRule.expect(DocumentGraphValidator.DocumentGraphException.class);
+        exceptionRule.expectMessage("Document dependency cycle detected: doc1->doc3->doc2->doc1.");
+        validator.validateDocumentGraph(documentListOf(schema1, schema2, schema3));
+    }
+
+    @Test
+    public void combined_inherit_and_ref_cycle_is_forbidden() {
+        Schema schema1 = createSearchWithName("doc1");
+        Schema schema2 = createSearchWithName("doc2", schema1);
+        Schema schema3 = createSearchWithName("doc3", schema2);
+        createDocumentReference(schema1, schema3, "ref_1");
+
+        DocumentGraphValidator validator = new DocumentGraphValidator();
+        exceptionRule.expect(DocumentGraphValidator.DocumentGraphException.class);
+        exceptionRule.expectMessage("Document dependency cycle detected: doc1->doc3->doc2->doc1.");
+        validator.validateDocumentGraph(documentListOf(schema1, schema2, schema3));
+    }
+
+    @Test
+    public void self_reference_is_forbidden() {
+        Schema adSchema = createSearchWithName("ad");
+        createDocumentReference(adSchema, adSchema, "ad_ref");
+
+        DocumentGraphValidator validator = new DocumentGraphValidator();
+        exceptionRule.expect(DocumentGraphValidator.DocumentGraphException.class);
+        exceptionRule.expectMessage("Document dependency cycle detected: ad->ad.");
+        validator.validateDocumentGraph(documentListOf(adSchema));
+    }
+
+    /**
+     * Self inheritance is checked early because it is possible, and because it otherwise
+     * produces a stack overflow before getting to graph validation.
+     */
+    @Test
+    public void self_inheritance_forbidden() {
+        try {
+            Schema adSchema = createSearchWithName("ad");
+            SDDocumentType document = adSchema.getDocument();
+            document.inherit(document);
+            fail("Expected exception");
+        }
+        catch (IllegalArgumentException e) {
+            assertEquals("Document type 'ad' cannot inherit itself", e.getMessage());
+        }
+    }
+
+    private static List<SDDocumentType> documentListOf(Schema... schemas) {
+        return Arrays.stream(schemas).map(Schema::getDocument).collect(toList());
+    }
+
+    private static Schema createSearchWithName(String name, Schema... parents) {
+        Schema campaignSchema = new Schema(name, MockApplicationPackage.createEmpty());
+        SDDocumentType document = new SDDocumentType(name);
+        campaignSchema.addDocument(document);
+        document.setDocumentReferences(new DocumentReferences(Collections.emptyMap()));
+        Arrays.stream(parents)
+                .map(Schema::getDocument)
+                .forEach(document::inherit);
+        return campaignSchema;
+    }
+
+    @SuppressWarnings("deprecation")
+    private static void createDocumentReference(Schema from, Schema to, String refFieldName) {
+        SDDocumentType fromDocument = from.getDocument();
+        SDField refField = new TemporarySDField(fromDocument, refFieldName, NewDocumentReferenceDataType.forDocumentName(to.getName()));
+        fromDocument.addField(refField);
+        Map<String, DocumentReference> originalMap = fromDocument.getDocumentReferences().get().referenceMap();
+        HashMap<String, DocumentReference> modifiedMap = new HashMap<>(originalMap);
+        modifiedMap.put(refFieldName, new DocumentReference(refField, to));
+        fromDocument.setDocumentReferences(new DocumentReferences(modifiedMap));
+    }
+}