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 java.util.Properties;
  
  import org.junit.jupiter.api.Test;
  
  public class PropertiesExpanderTest {
  
      @Test
      public void testCtorException() {
          try {
              final Object test = new PropertiesExpander(null);
              assertWithMessage("exception expected but got " + test).fail();
          }
          catch (IllegalArgumentException ex) {
              assertWithMessage("Invalid exception message")
                      .that(ex.getMessage())
                      .isEqualTo("cannot pass null");
          }
      }
  
      @Test
      public void testDefaultProperties() {
          final Properties properties = new Properties(System.getProperties());
          properties.setProperty("test", "checkstyle");
          final String propertiesUserHome = properties.getProperty("user.home");
          assertWithMessage("Invalid user.home property")
                  .that(propertiesUserHome)
                  .isEqualTo(System.getProperty("user.home"));
          assertWithMessage("Invalid checkstyle property")
                  .that(properties.getProperty("test"))
                  .isEqualTo("checkstyle");
  
          final PropertiesExpander expander = new PropertiesExpander(properties);
          final String expanderUserHome = expander.resolve("user.home");
          assertWithMessage("Invalid user.home property")
                  .that(expanderUserHome)
                  .isEqualTo(System.getProperty("user.home"));
          assertWithMessage("Invalid checkstyle property")
                  .that(expander.resolve("test"))
                  .isEqualTo("checkstyle");
      }
  
  }
  