- Updated test names to reflect what it is testing

libraries-2/src/test/java/com/baeldung/mapdb/CollectionsUnitTest.java

@@ -0,0 +1,33 @@
+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<String> set = db.
+          treeSet("mySet")
+          .serializer(Serializer.STRING)
+          .createOrOpen();
+
+        String myString = "Baeldung!";
+
+        set.add(myString);
+        set.add(myString);
+
+        assertEquals(1, set.size());
+
+        db.close();
+    }
+}