[MNG-7375] prevent potential NPE in Metadata.merge(...)

Add unit tests for merge

maven-repository-metadata/src/main/mdo/metadata.mdo

@@ -97,7 +97,7 @@ under the License.
 
  for ( Plugin preExisting : getPlugins() )
  {
- if ( preExisting.getPrefix().equals( plugin.getPrefix() ) )
+ if ( java.util.Objects.equals( preExisting.getPrefix(), plugin.getPrefix() ) )
  {
  found = true;
  break;

maven-repository-metadata/src/test/java/org/apache/maven/artifact/repository/metadata/MetadataTest.java

@@ -0,0 +1,82 @@
+package org.apache.maven.artifact.repository.metadata;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class MetadataTest {
+
+ @Test
+ void testMergeWithEmptyMetadata() {
+ Metadata metadata = new Metadata();
+
+ Metadata newMetadata = new Metadata();
+ Assertions.assertFalse(metadata.merge(newMetadata));
+ }
+
+ @Test
+ void testMergeWithDifferentPrefixes() {
+ Metadata metadata = new Metadata();
+ Plugin plugin = new Plugin();
+ plugin.setArtifactId("myArtifactId");
+ plugin.setName("My Name");
+ plugin.setPrefix("myprefix");
+ metadata.addPlugin(plugin);
+
+ Metadata newMetadata = new Metadata();
+ Plugin newPlugin = plugin.clone();
+ newPlugin.setArtifactId("myNewArtifactId");
+ plugin.setPrefix("mynewprefix");
+ newMetadata.addPlugin(newPlugin);
+ Assertions.assertTrue(metadata.merge(newMetadata));
+ }
+
+ @Test
+ void testMergeWithSamePrefixAndDifferentArtifactIds() {
+ Metadata metadata = new Metadata();
+ Plugin plugin = new Plugin();
+ plugin.setArtifactId("myArtifactId");
+ plugin.setName("My Name");
+ plugin.setPrefix("myprefix");
+ metadata.addPlugin(plugin);
+
+ Metadata newMetadata = new Metadata();
+ Plugin newPlugin = plugin.clone();
+ newPlugin.setArtifactId("myNewArtifactId");
+ newMetadata.addPlugin(newPlugin);
+ Assertions.assertFalse(metadata.merge(newMetadata));
+ }
+
+ @Test
+ void testMergeWithEmptyPrefix() {
+ Metadata metadata = new Metadata();
+ Plugin plugin = new Plugin();
+ plugin.setArtifactId("myArtifactId");
+ plugin.setName("My Name");
+ metadata.addPlugin(plugin);
+
+ Metadata newMetadata = new Metadata();
+ Plugin newPlugin = plugin.clone();
+ newPlugin.setPrefix("myprefix");
+ newMetadata.addPlugin(newPlugin);
+ Assertions.assertTrue(metadata.merge(newMetadata));
+ }
+}