package com.baeldung.mapdb; import org.junit.Test; import org.mapdb.DB; import org.mapdb.DBMaker; import org.mapdb.Serializer; import java.util.NavigableSet; import static junit.framework.Assert.assertEquals; public class CollectionsUnitTest { @Test public void givenSetCreatedInDB_whenMultipleElementsAdded_checkOnlyOneExists() { DB db = DBMaker.memoryDB().make(); NavigableSet set = db. treeSet("mySet") .serializer(Serializer.STRING) .createOrOpen(); String myString = "Baeldung!"; set.add(myString); set.add(myString); assertEquals(1, set.size()); db.close(); } }