Add a test wrt #214

Author: cowtowncoder

datatypes/src/test/java/com/fasterxml/jackson/datatype/jdk8/OptionalMergeTest.java

@@ -0,0 +1,33 @@
+package com.fasterxml.jackson.datatype.jdk8;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Optional;
+
+import com.fasterxml.jackson.annotation.JsonMerge;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+public class OptionalMergeTest extends ModuleTestBase
+{
+    // [modules-java8#214]
+    static class OptionalListWrapper {
+        @JsonMerge
+        public Optional<List<String>> list;
+    }
+
+    private final ObjectMapper MAPPER = mapperWithModule();
+
+    // [modules-java8#214]: ReferenceType of List, merge
+    public void testMergeToListViaRef() throws Exception
+    {
+        OptionalListWrapper base = MAPPER.readValue(a2q("{'list':['a']}"),
+                OptionalListWrapper.class);
+        assertNotNull(base.list);
+        assertEquals(Arrays.asList("a"), base.list.get());
+
+        OptionalListWrapper merged = MAPPER.readerForUpdating(base)
+                .readValue(a2q("{'list':['b']}"));
+        assertSame(base, merged);
+        assertEquals(Arrays.asList("a", "b"), base.list.get());
+    }
+}