Add failing test for #4047

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

@@ -73,10 +73,9 @@ static class TestCommandChild extends TestCommandParent { }
     /**********************************************************
      */
 
-    final ObjectMapper WRAP_ROOT_MAPPER = new ObjectMapper();
-    {
-        WRAP_ROOT_MAPPER.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
-    }
+    private final ObjectMapper WRAP_ROOT_MAPPER = jsonMapperBuilder()
+            .configure(SerializationFeature.WRAP_ROOT_VALUE, true)
+            .build();
 
     @SuppressWarnings("unchecked")
     public void testSuperClass() throws Exception

src/test/java/com/fasterxml/jackson/failing/TestRootType4047Test.java

@@ -0,0 +1,59 @@
+package com.fasterxml.jackson.failing;
+
+import com.fasterxml.jackson.annotation.JsonRootName;
+import com.fasterxml.jackson.databind.BaseMapTest;
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+
+// [databind#4047] : ObjectMapper.valueToTree will ignore the configuration SerializationFeature.WRAP_ROOT_VALUE
+public class TestRootType4047Test extends BaseMapTest {
+
+    @JsonRootName("event")
+    static class Event {
+        public Long id;
+        public String name;
+    }
+
+    /*
+    /**********************************************************
+    /* Main tests
+    /**********************************************************
+     */
+
+    private final String WRAPPED_EVENT_JSON = "{\"event\":{\"id\":1,\"name\":\"foo\"}}";
+    private final String UNWRAPPED_EVENT_JSON = "{\"id\":1,\"name\":\"foo\"}";
+
+    public void testValueToTree() throws Exception {
+        // Arrange
+        final ObjectMapper WRAP_ROOT_MAPPER = jsonMapperBuilder()
+                .enable(SerializationFeature.WRAP_ROOT_VALUE)
+                .build();
+        Event value = new Event();
+        value.id = 1L;
+        value.name = "foo";
+
+        // (1) works
+        assertEquals(WRAPPED_EVENT_JSON,
+                WRAP_ROOT_MAPPER.writeValueAsString(value));
+
+        // (2) fails w/ {"id":1,"name":"foo"}
+        assertEquals(WRAPPED_EVENT_JSON,
+                WRAP_ROOT_MAPPER.valueToTree(value).toString());
+    }
+
+    public void testTreeToValue() throws Exception {
+        // Arrange
+        final ObjectMapper UNWRAP_MAPPER = jsonMapperBuilder()
+                .enable(DeserializationFeature.UNWRAP_ROOT_VALUE)
+                .build();
+
+        /*
+         * (1) both fails with
+         * com.fasterxml.jackson.databind.exc.MismatchedInputException: Root name ('event') does not match expected ('JsonNode') for type `com.fasterxml.jackson.databind.JsonNode`
+         *  at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 2] (through reference chain: com.fasterxml.jackson.databind.JsonNode["event"])
+         */
+        UNWRAP_MAPPER.readTree(WRAPPED_EVENT_JSON);
+        UNWRAP_MAPPER.readTree(UNWRAPPED_EVENT_JSON);
+    }
+}