add cyclic data serialization tests

src/test/java/com/fasterxml/jackson/databind/ser/CyclicTypeSerTest.java

@@ -17,7 +17,7 @@
 public class CyclicTypeSerTest
     extends BaseMapTest
 {
-    static class Bean
+    public static class Bean
     {
         Bean _next;
         final String _name;

src/test/java/com/fasterxml/jackson/databind/ser/dos/CyclicDataSerTest.java

@@ -0,0 +1,47 @@
+package com.fasterxml.jackson.databind.ser.dos;
+
+import com.fasterxml.jackson.core.StreamWriteConstraints;
+import com.fasterxml.jackson.databind.BaseMapTest;
+import com.fasterxml.jackson.databind.JsonMappingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.exc.InvalidDefinitionException;
+import com.fasterxml.jackson.databind.ser.CyclicTypeSerTest;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Simple unit tests to verify that we fail gracefully if you attempt to serialize
+ * data that is cyclic (eg a list that contains itself).
+ */
+public class CyclicDataSerTest
+    extends BaseMapTest
+{
+    private final ObjectMapper MAPPER = newJsonMapper();
+
+    public void testLinkedAndCyclic() throws Exception {
+        CyclicTypeSerTest.Bean bean = new CyclicTypeSerTest.Bean(null, "last");
+        bean.assignNext(bean);
+        try {
+            writeAndMap(MAPPER, bean);
+            fail("expected InvalidDefinitionException");
+        } catch (InvalidDefinitionException idex) {
+            assertTrue("InvalidDefinitionException message is as expected?",
+                    idex.getMessage().startsWith("Direct self-reference leading to cycle"));
+        }
+    }
+
+    public void testListWithSelfReference() throws Exception {
+        List<Object> list = new ArrayList<>();
+        list.add(list);
+        try {
+            writeAndMap(MAPPER, list);
+            fail("expected JsonMappingException");
+        } catch (JsonMappingException jmex) {
+            String exceptionPrefix = String.format("Document nesting depth (%d) exceeds the maximum allowed",
+                    StreamWriteConstraints.DEFAULT_MAX_DEPTH + 1);
+            assertTrue("JsonMappingException message is as expected?",
+                    jmex.getMessage().startsWith(exceptionPrefix));
+        }
+    }
+}