add unit test

tests-on-jvm/src/com/fsck/k9/helper/UtilityTest.java

@@ -0,0 +1,28 @@
+package com.fsck.k9.mail.internet;
+
+import com.fsck.k9.helper.Utility;
+
+import junit.framework.TestCase;
+
+import java.io.Serializable;
+import java.util.LinkedList;
+
+public class UtilityTest extends TestCase {
+
+    public void testToSerializableList() {
+        LinkedList<String> input = new LinkedList<String>(Arrays.asList("a", "b"));
+
+        Serializable serializableList = Utility.toSerializableList(input);
+
+        assertEquals(serializableList, input);
+    }
+
+    public void testToSerializableListAlreadySerializable() {
+        ArrayList<String> input = new ArrayList<String>(Arrays.asList("a", "b"));
+
+        Serializable serializableList = Utility.toSerializableList(input);
+
+        assertSame(serializableList, input);
+    }
+
+}