added delete collection and test

src/main/java/it/inaf/oats/vospace/persistence/CollectionsDAO.java

@@ -43,7 +43,7 @@ public class CollectionsDAO {
         });
     }
 
-    Optional<NodeCollection> getNodeCollectionById(Long id) {
+    public Optional<NodeCollection> getNodeCollectionById(Long id) {
         String sql = "SELECT collection_id, title, owner_id FROM collections\n"
                 + "WHERE collection_id = ?";
 
@@ -66,7 +66,7 @@ public class CollectionsDAO {
 
     }
     
-    List<NodeCollection> getUserNodeCollections(String userId) {
+    public List<NodeCollection> getUserNodeCollections(String userId) {
         String sql = "SELECT collection_id, title, owner_id FROM collections\n"
                 + "WHERE owner_id = ?";
 
@@ -83,6 +83,13 @@ public class CollectionsDAO {
         return nc;
     }
     
+    public void deleteCollection(Long collectionId) {
+        // TODO: this is just a stub for development.
+        String sql  = "DELETE FROM collections WHERE collection_id = ?";
+        
+        jdbcTemplate.update(sql, collectionId);
+    }
+
     private NodeCollection getNodeCollectionFromResultset(ResultSet rs)
             throws SQLException {
         NodeCollection nc = new NodeCollection(

src/test/java/it/inaf/oats/vospace/persistence/CollectionsDAOTest.java

@@ -5,6 +5,8 @@
  */
 package it.inaf.oats.vospace.persistence;
 
+import it.inaf.oats.vospace.persistence.model.NodeCollection;
+import java.util.List;
 import javax.sql.DataSource;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -43,7 +45,18 @@ public class CollectionsDAOTest {
         collectionsDAO.createNewCollection("collection1", "pippo");
         collectionsDAO.createNewCollection("collection2", "pippo");
         
-        assertEquals(2, collectionsDAO.getUserNodeCollections("pippo").size());
+        List<NodeCollection> ncl = 
+                collectionsDAO.getUserNodeCollections("pippo");
+        
+        assertEquals(2, ncl.size());
+        
+        for(NodeCollection nc : ncl) {
+            collectionsDAO.deleteCollection(
+                    nc.getId()
+            );            
+        }
+        
+        assertTrue(collectionsDAO.getUserNodeCollections("pippo").isEmpty());        
     }