code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle;
  
  import static com.google.common.truth.Truth.assertWithMessage;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URL;
  import java.net.URLConnection;
  import java.net.URLStreamHandler;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.Set;
  
  import org.junit.jupiter.api.Test;
  import org.xml.sax.SAXException;
  
  import com.puppycrawl.tools.checkstyle.api.CheckstyleException;
  
  /**
   * Tests loading of package names from XML files.
   *
   * @noinspection ClassLoaderInstantiation
   * @noinspectionreason ClassLoaderInstantiation - Custom class loader is needed to pass URLs to
   *      pretend these are loaded from the classpath though we can't add/change the files for
   *      testing. The class loader is nested in this class, so the custom class loader we
   *      are using is safe.
   */
  public class PackageNamesLoaderTest extends AbstractPathTestSupport {
  
      @Override
      protected String getPackageLocation() {
          return "com/puppycrawl/tools/checkstyle/packagenamesloader";
      }
  
      @Test
      public void testDefault()
              throws CheckstyleException {
          final Set<String> packageNames = PackageNamesLoader
                  .getPackageNames(Thread.currentThread()
                          .getContextClassLoader());
          assertWithMessage("pkgNames.length.")
              .that(packageNames)
              .isEmpty();
      }
  
      @Test
      public void testNoPackages() throws Exception {
          final Set<String> actualPackageNames = PackageNamesLoader
                  .getPackageNames(new TestUrlsClassLoader(Collections.emptyEnumeration()));
  
          assertWithMessage("Invalid package names length.")
              .that(actualPackageNames)
              .isEmpty();
      }
  
      @Test
      public void testPackagesFile() throws Exception {
          final Enumeration<URL> enumeration = Collections.enumeration(Collections.singleton(
                  new File(getPath("InputPackageNamesLoaderFile.xml")).toURI().toURL()));
  
          final Set<String> actualPackageNames = PackageNamesLoader
                  .getPackageNames(new TestUrlsClassLoader(enumeration));
          final String[] expectedPackageNames = {
              "com.puppycrawl.tools.checkstyle",
              "com.puppycrawl.tools.checkstyle.checks",
              "com.puppycrawl.tools.checkstyle.checks.annotation",
              "com.puppycrawl.tools.checkstyle.checks.blocks",
              "com.puppycrawl.tools.checkstyle.checks.coding",
              "com.puppycrawl.tools.checkstyle.checks.design",
              "com.puppycrawl.tools.checkstyle.checks.header",
              "com.puppycrawl.tools.checkstyle.checks.imports",
              "com.puppycrawl.tools.checkstyle.checks.indentation",
              "com.puppycrawl.tools.checkstyle.checks.javadoc",
              "com.puppycrawl.tools.checkstyle.checks.metrics",
              "com.puppycrawl.tools.checkstyle.checks.modifier",
              "com.puppycrawl.tools.checkstyle.checks.naming",
              "com.puppycrawl.tools.checkstyle.checks.regexp",
              "com.puppycrawl.tools.checkstyle.checks.sizes",
              "com.puppycrawl.tools.checkstyle.checks.whitespace",
              "com.puppycrawl.tools.checkstyle.filefilters",
              "com.puppycrawl.tools.checkstyle.filters",
          };
  
          assertWithMessage("Invalid package names length.")
              .that(actualPackageNames)
              .hasSize(expectedPackageNames.length);
          final Set<String> checkstylePackagesSet =
                  new HashSet<>(Arrays.asList(expectedPackageNames));
          assertWithMessage("Invalid names set.")
              .that(actualPackageNames)
              .isEqualTo(checkstylePackagesSet);
      }
  
      @Test
      public void testPackagesWithDots() throws Exception {
          final Enumeration<URL> enumeration = Collections.enumeration(Collections.singleton(
                  new File(getPath("InputPackageNamesLoaderWithDots.xml")).toURI().toURL()));
  
          final Set<String> actualPackageNames = PackageNamesLoader
                  .getPackageNames(new TestUrlsClassLoader(enumeration));
          final String[] expectedPackageNames = {
              "coding.",
          };
  
          assertWithMessage("Invalid package names length.")
              .that(actualPackageNames)
              .hasSize(expectedPackageNames.length);
          final Set<String> checkstylePackagesSet =
                  new HashSet<>(Arrays.asList(expectedPackageNames));
          assertWithMessage("Invalid names set.")
              .that(actualPackageNames)
              .isEqualTo(checkstylePackagesSet);
      }
  
      @Test
      public void testPackagesWithDotsEx() throws Exception {
          final Enumeration<URL> enumeration = Collections.enumeration(Collections.singleton(
                  new File(getPath("InputPackageNamesLoaderWithDotsEx.xml")).toURI().toURL()));
  
          final Set<String> actualPackageNames = PackageNamesLoader
                  .getPackageNames(new TestUrlsClassLoader(enumeration));
          final String[] expectedPackageNames = {
              "coding.specific",
              "coding.",
          };
  
          assertWithMessage("Invalid package names length.")
              .that(actualPackageNames)
              .hasSize(expectedPackageNames.length);
          final Set<String> checkstylePackagesSet =
                  new HashSet<>(Arrays.asList(expectedPackageNames));
          assertWithMessage("Invalid names set.")
              .that(actualPackageNames)
              .isEqualTo(checkstylePackagesSet);
      }
  
      @Test
      public void testPackagesWithSaxException() throws Exception {
          final Enumeration<URL> enumeration = Collections.enumeration(Collections.singleton(
                  new File(getPath("InputPackageNamesLoaderNotXml.java")).toURI().toURL()));
  
          try {
              PackageNamesLoader.getPackageNames(new TestUrlsClassLoader(enumeration));
              assertWithMessage("CheckstyleException is expected").fail();
          }
          catch (CheckstyleException ex) {
              assertWithMessage("Invalid exception cause class")
                      .that(ex)
                      .hasCauseThat()
                      .isInstanceOf(SAXException.class);
          }
      }
  
      @Test
      public void testPackagesWithIoException() throws Exception {
          final URLConnection urlConnection = new URLConnection(null) {
              @Override
              public void connect() {
                  // no code
              }
  
              @Override
              public InputStream getInputStream() {
                  return null;
              }
          };
          final URL url = new URL("test", null, 0, "", new URLStreamHandler() {
              @Override
              protected URLConnection openConnection(URL u) {
                  return urlConnection;
              }
          });
  
          final Enumeration<URL> enumeration = Collections.enumeration(Collections.singleton(url));
  
          try {
              PackageNamesLoader.getPackageNames(new TestUrlsClassLoader(enumeration));
              assertWithMessage("CheckstyleException is expected").fail();
          }
          catch (CheckstyleException ex) {
              assertWithMessage("Invalid exception cause class")
                      .that(ex)
                      .hasCauseThat()
                      .isInstanceOf(IOException.class);
              assertWithMessage("Invalid exception message")
                      .that(ex)
                      .hasMessageThat()
                      .isNotEqualTo("unable to get package file resources");
          }
      }
  
      @Test
      public void testPackagesWithIoExceptionGetResources() {
          try {
              PackageNamesLoader.getPackageNames(new TestIoExceptionClassLoader());
              assertWithMessage("CheckstyleException is expected").fail();
          }
          catch (CheckstyleException ex) {
              assertWithMessage("Invalid exception cause class")
                      .that(ex)
                      .hasCauseThat()
                      .isInstanceOf(IOException.class);
              assertWithMessage("Invalid exception message")
                  .that(ex.getMessage())
                  .isEqualTo("unable to get package file resources");
          }
      }
  
      @Test
      public void testUnmodifiableCollection() throws Exception {
          final Set<String> actualPackageNames = PackageNamesLoader
                  .getPackageNames(new TestUrlsClassLoader(Collections.emptyEnumeration()));
  
          assertThrows(UnsupportedOperationException.class,
                  () -> actualPackageNames.add("com.puppycrawl.tools.checkstyle.checks.modifier"));
  
      }
  
      @Test
      public void testMapping() throws Exception {
          final Enumeration<URL> enumeration = Collections.enumeration(Collections.singleton(
                  new File(getPath("InputPackageNamesLoader1.xml")).toURI().toURL()));
  
          final Set<String> actualPackageNames = PackageNamesLoader
                  .getPackageNames(new TestUrlsClassLoader(enumeration));
  
          assertWithMessage("Invalid package names length.")
              .that(actualPackageNames)
              .hasSize(3);
      }
  
      @Test
      public void testMapping2() throws Exception {
          final Enumeration<URL> enumeration = Collections.enumeration(Collections.singleton(
                  new File(getPath("InputPackageNamesLoader2.xml")).toURI().toURL()));
  
          final Set<String> actualPackageNames = PackageNamesLoader
                  .getPackageNames(new TestUrlsClassLoader(enumeration));
  
          assertWithMessage("Invalid package names length.")
              .that(actualPackageNames)
              .hasSize(3);
      }
  
      /**
       * Mocked ClassLoader for testing URL loading.
       *
       * @noinspection CustomClassloader
       * @noinspectionreason CustomClassloader - needed to pass URLs to pretend these are loaded
       *      from the classpath though we can't add/change the files for testing
       */
      private static final class TestUrlsClassLoader extends ClassLoader {
  
          private final Enumeration<URL> urls;
  
          private TestUrlsClassLoader(Enumeration<URL> urls) {
              this.urls = urls;
          }
  
          @Override
          public Enumeration<URL> getResources(String name) {
              return urls;
          }
      }
  
      /**
       * Mocked ClassLoader for testing exceptions.
       *
       * @noinspection CustomClassloader
       * @noinspectionreason CustomClassloader - needed to throw an exception to
       *      test a catch statement
       */
      private static final class TestIoExceptionClassLoader extends ClassLoader {
          @Override
          public Enumeration<URL> getResources(String name) throws IOException {
              throw new IOException("test");
          }
      }
  
  }
  