[MNG-6326] Make the build fail if core extensions can not be loaded

core-it-suite/src/test/java/org/apache/maven/it/IntegrationTestSuite.java

@@ -106,6 +106,7 @@ public static Test suite()
         // Tests that don't run stable and need to be fixed
         // -------------------------------------------------------------------------------------------------------------
         // suite.addTestSuite( MavenIT0108SnapshotUpdateTest.class ); -- MNG-3137
+        suite.addTestSuite( MavenITmng6326CoreExtensionsNotFoundTest.class );
         suite.addTestSuite( MavenITmng5561PluginRelocationLosesConfigurationTest.class );
         suite.addTestSuite( MavenITmng7335MissingJarInParallelBuild.class );
         suite.addTestSuite( MavenITmng4463DependencyManagementImportVersionRanges.class );

core-it-suite/src/test/java/org/apache/maven/it/MavenITmng6326CoreExtensionsNotFoundTest.java

@@ -0,0 +1,74 @@
+package org.apache.maven.it;
+
+/*
+ * 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 java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+
+import org.apache.maven.it.util.ResourceExtractor;
+
+/**
+ * This is a test set for <a href="https://issues.apache.org/jira/browse/MNG-6326">MNG-6326</a>:
+ * check that Maven fails if it cannot load core extensions contributed by <code>.mvn/extensions.xml</code>.
+ */
+public class MavenITmng6326CoreExtensionsNotFoundTest
+    extends AbstractMavenIntegrationTestCase
+{
+    public MavenITmng6326CoreExtensionsNotFoundTest()
+    {
+        super( "[3.8.5,)" );
+    }
+
+    public void testCoreExtensionsNotFound()
+        throws Exception
+    {
+        File testDir = ResourceExtractor.simpleExtractResources( getClass(), "/mng-6326-core-extensions-not-found" );
+
+        Verifier verifier = newVerifier( testDir.getAbsolutePath() );
+        try
+        {
+            verifier.executeGoal( "validate" );
+            fail( "should have failed ");
+        }
+        catch ( VerificationException e )
+        {
+            try
+            {
+                verifier.verifyTextInLog( "[ERROR] Error executing Maven." );
+                verifier.verifyTextInLog( "Extension org.apache.maven.its.it-core-extensions:maven-it-unknown-extensions:0.1 or one of its dependencies could not be resolved" );
+            }
+            catch ( VerificationException e2 )
+            {
+                throw new VerificationException( e2.getMessage() + "\nLog:" + getLogContent( verifier ) );
+            }
+        }
+    }
+
+    private String getLogContent( Verifier verifier ) throws IOException
+    {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        Files.copy( Paths.get( verifier.getBasedir(), verifier.getLogFileName() ), baos );
+        return baos.toString();
+    }
+
+}

core-it-suite/src/test/resources/mng-6326-core-extensions-not-found/.mvn/extensions.xml

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!--
+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.
+-->
+
+<extensions>
+  <extension>
+    <groupId>org.apache.maven.its.it-core-extensions</groupId>
+    <artifactId>maven-it-unknown-extensions</artifactId>
+    <version>0.1</version>
+  </extension>
+</extensions>

core-it-suite/src/test/resources/mng-6326-core-extensions-not-found/pom.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!--
+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.
+-->
+
+<project>
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.apache.maven.its.it-core-extensions</groupId>
+  <artifactId>test</artifactId>
+  <version>0.1</version>
+  <packaging>jar</packaging>
+
+  <name>Maven Integration Test :: it-core-extensions</name>
+  <description>
+    Verify that Maven loads core extensions and components contributed by the extensions are available to regular
+    plugins.
+  </description>
+
+</project>