add a failing test for #1391

Author: cowtowncoder

src/test/java/com/fasterxml/jackson/failing/DefaultTypingOverride1391Test.java

@@ -0,0 +1,38 @@
+package com.fasterxml.jackson.failing;
+
+import java.util.*;
+
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import com.fasterxml.jackson.databind.*;
+
+// [databind#1391]
+public class DefaultTypingOverride1391Test extends BaseMapTest
+{
+    final static ObjectMapper WITH_OBJECT_AND_NON_CONCRETE = new ObjectMapper().enableDefaultTypingAsProperty(
+            ObjectMapper.DefaultTyping.OBJECT_AND_NON_CONCRETE, "$type");
+
+    final static ObjectMapper PLAIN_OBJECT_MAPPER = new ObjectMapper();
+
+    static class MyClass {
+
+        private final SortedSet<String> treeSetStrings = new TreeSet<>();
+
+        @JsonTypeInfo(use = JsonTypeInfo.Id.NONE)
+        public SortedSet<String> getTreeSetStrings() {
+            return this.treeSetStrings;
+        }
+    }
+
+    public void testCollectionTyping() throws Exception {
+
+        final MyClass toSerialize = new MyClass();
+
+        final String fromPlainObjectMapper = PLAIN_OBJECT_MAPPER.writeValueAsString(toSerialize);
+        System.out.println("\nfrom plain ObjectMapper:\n" + fromPlainObjectMapper);
+
+        final String fromObjectMapperWithDefaultTyping = WITH_OBJECT_AND_NON_CONCRETE.writeValueAsString(toSerialize);
+        System.out.println("\nfrom ObjectMapper with default typing:\n" + fromObjectMapperWithDefaultTyping);
+
+        assertEquals(fromPlainObjectMapper, fromObjectMapperWithDefaultTyping);
+    }
+}