Try to modify an existing test to help resolve #4354

src/test/java/com/fasterxml/jackson/databind/jsontype/ext/ExternalTypeId2588Test.java

@@ -9,18 +9,25 @@
 import com.fasterxml.jackson.databind.jsontype.impl.TypeIdResolverBase;
 import com.fasterxml.jackson.databind.testutil.DatabindTestUtil;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 
-// [databind#2588] / [databind#2610]
+// [databind#2588] / [databind#2610] / [databind#4354]
 public class ExternalTypeId2588Test extends DatabindTestUtil
 {
  // [databind#2588]
  interface Animal { }
 
- static class Cat implements Animal { }
+ static class Cat implements Animal {
+ public int lives = 9;
+ }
 
  public static class Dog implements Animal { }
 
+ static class Wolf implements Animal {
+ public boolean alive;
+ }
+
  @JsonIgnoreProperties(ignoreUnknown = true)
  static class Pet {
  final String type;
@@ -51,6 +58,8 @@ public String idFromValueAndType(Object value, Class<?> suggestedType) {
  return "cat";
  } else if (suggestedType.isAssignableFrom(Dog.class)) {
  return "dog";
+ } else if (suggestedType.isAssignableFrom(Wolf.class)) {
+ return "wolf";
  }
  return null;
  }
@@ -71,16 +80,17 @@ public JsonTypeInfo.Id getMechanism() {
  }
  }
 
+ private final ObjectMapper MAPPER = newJsonMapper();
+
  // [databind#2588]
  @Test
- public void testExternalTypeId2588() throws Exception
+ public void testExternalTypeId2588Read() throws Exception
  {
- final ObjectMapper mapper = newJsonMapper();
  Pet pet;
 
  // works?
 
- pet = mapper.readValue(a2q(
+ pet = MAPPER.readValue(a2q(
 "{\n" +
 " 'type': 'cat',\n" +
 " 'animal': { },\n" +
@@ -92,7 +102,7 @@ public void testExternalTypeId2588() throws Exception
  assertNotNull(pet);
 
  // fails:
- pet = mapper.readValue(a2q(
+ pet = MAPPER.readValue(a2q(
 "{\n" +
 " 'animal\": { },\n" +
 " 'ignoredObject': {\n" +
@@ -103,4 +113,11 @@ public void testExternalTypeId2588() throws Exception
  ), Pet.class);
  assertNotNull(pet);
  }
+
+ @Test
+ public void testExternalTypeId2588Write() throws Exception
+ {
+ String json = MAPPER.writeValueAsString(new Pet("cat", new Wolf()));
+ assertEquals(a2q("{'animal':{'alive':false},'type':'wolf'}"), json);
+ }
 }