code: ///////////////////////////////////////////////////////////////////////////
  //                   __                _      _   ________               //
  //                  / /   ____  ____ _(_)____/ | / / ____/               //
  //                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
  //                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
  //               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
  //                           /____/                                      //
  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  Copyright 2015-20xx Christoph Zengler                                //
  //                                                                       //
  //  Licensed 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.                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  
  package org.logicng.graphs.datastructures;
  
  import static org.assertj.core.api.Assertions.assertThat;
  
  import org.junit.jupiter.api.Test;
  
  /**
   * Unit tests for {@link HypergraphNode}.
   * @version 1.4.0
   * @since 1.4.0
   */
  public class HypergraphNodeTest {
  
      @Test
      public void testSimpleMethods() {
          final Hypergraph<String> hypergraph = new Hypergraph<>();
          final HypergraphNode<String> node1 = new HypergraphNode<>(hypergraph, "A");
          final HypergraphNode<String> node2 = new HypergraphNode<>(hypergraph, "B");
          final HypergraphEdge<String> edge1 = new HypergraphEdge<>(node1, node2);
          assertThat(node1.graph()).isEqualTo(hypergraph);
          assertThat(node1.content()).isEqualTo("A");
          assertThat(node1.edges()).containsExactlyInAnyOrder(edge1);
      }
  
      @Test
      public void testEquals() {
          final Hypergraph<String> hypergraph = new Hypergraph<>();
          final HypergraphNode<String> node1 = new HypergraphNode<>(hypergraph, "A");
          final HypergraphNode<String> node2 = new HypergraphNode<>(hypergraph, "B");
          final HypergraphNode<String> node3 = new HypergraphNode<>(hypergraph, "A");
  
          assertThat(node1.equals(null)).isFalse();
          assertThat(node1).isNotEqualTo(42);
  
          assertThat(node1).isEqualTo(node1);
          assertThat(node1.equals(node1)).isTrue();
          assertThat(node1).isEqualTo(node3);
          assertThat(node3).isEqualTo(node1);
          assertThat(node1).isNotEqualTo(node2);
          assertThat(node2).isNotEqualTo(node1);
      }
  }
  