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.formulas;
  
  import static org.assertj.core.api.Assertions.assertThat;
  
  import org.junit.jupiter.api.Test;
  import org.logicng.TestWithExampleFormulas;
  import org.logicng.datastructures.Substitution;
  
  /**
   * Unit Tests for the class {@link Literal}.
   * @version 2.3.0
   * @since 1.0
   */
  public class LiteralTest extends TestWithExampleFormulas {
  
      @Test
      public void testType() {
          assertThat(this.A.type()).isEqualTo(FType.LITERAL);
          assertThat(this.NA.type()).isEqualTo(FType.LITERAL);
      }
  
      @Test
      public void testShortcutCreators() {
          assertThat(this.f.literal("a", true) == this.f.variable("a")).isTrue();
          assertThat(this.f.literal("name", true) == this.f.variable("name")).isTrue();
      }
  
      @Test
      public void testNegation() {
          assertThat(this.A.negate() == this.NA).isTrue();
          assertThat(this.NA.negate() == this.A).isTrue();
      }
  
      @Test
      public void testGetters() {
          assertThat(this.A.name()).isEqualTo("a");
          assertThat(this.NA.name()).isEqualTo("a");
          assertThat(this.A.phase()).isEqualTo(true);
          assertThat(this.NA.phase()).isEqualTo(false);
      }
  
      @Test
      public void testVariables() {
          assertThat(this.A.variables())
                  .hasSize(1)
                  .containsExactly(this.A);
          assertThat(this.NA.variables())
                  .hasSize(1)
                  .containsExactly(this.A);
      }
  
      @Test
      public void testLiterals() {
          assertThat(this.A.literals())
                  .hasSize(1)
                  .containsExactly(this.A);
          assertThat(this.NA.literals())
                  .hasSize(1)
                  .containsExactly(this.NA);
      }
  
      @Test
      public void testExpSubstitution() {
          final Substitution substitution = new Substitution();
          substitution.addMapping(this.f.variable("a"), this.f.literal("b", false));
          substitution.addMapping(this.f.variable("c"), this.f.variable("d"));
          substitution.addMapping(this.f.variable("x"), this.f.and(this.f.variable("y"), this.f.variable("z")));
      }
  
      @Test
      public void testToString() {
          assertThat(this.A.toString()).isEqualTo("a");
          assertThat(this.NA.toString()).isEqualTo("~a");
      }
  
      @Test
      public void testEquals() {
          assertThat(this.f.literal("a", true).equals(this.A)).isTrue();
          assertThat(this.f.literal("a", false).equals(this.NA)).isTrue();
          assertThat(this.A.equals(this.A)).isTrue();
          assertThat(this.B.equals(this.A)).isFalse();
          assertThat(this.NA.equals(this.A)).isFalse();
          assertThat(this.f.falsum()).isNotEqualTo(this.A);
      }
  
      @Test
      public void testEqualsDifferentFormulaFactory() {
          assertThat(this.g.literal("a", true).equals(this.A)).isTrue();
          assertThat(this.g.literal("a", false).equals(this.NA)).isTrue();
          assertThat(this.g.literal("a", false).equals(this.A)).isFalse();
          assertThat(this.g.literal("b", true).equals(this.A)).isFalse();
          assertThat(this.g.falsum()).isNotEqualTo(this.A);
      }
  
      @Test
      public void testCompareTo() {
          assertThat(this.A.compareTo(this.A) == 0).isTrue();
          assertThat(this.NA.compareTo(this.NA) == 0).isTrue();
          assertThat(this.A.compareTo(this.NA) < 0).isTrue();
          assertThat(this.A.compareTo(this.NB) < 0).isTrue();
          assertThat(this.A.compareTo(this.B) < 0).isTrue();
          assertThat(this.A.compareTo(this.X) < 0).isTrue();
          assertThat(this.NA.compareTo(this.NX) < 0).isTrue();
      }
  
      @Test
      public void testHash() {
          assertThat(this.f.literal("a", true).hashCode()).isEqualTo(this.A.hashCode());
          assertThat(this.f.literal("a", false).hashCode()).isEqualTo(this.NA.hashCode());
      }
  
      @Test
      public void testNumberOfAtoms() {
          assertThat(this.A.numberOfAtoms()).isEqualTo(1);
          assertThat(this.NA.numberOfAtoms()).isEqualTo(1);
          assertThat(this.NA.numberOfAtoms()).isEqualTo(1);
      }
  
      @Test
      public void testNumberOfNodes() {
          assertThat(this.A.numberOfNodes()).isEqualTo(1);
          assertThat(this.NA.numberOfNodes()).isEqualTo(1);
          assertThat(this.NA.numberOfNodes()).isEqualTo(1);
      }
  
      @Test
      public void testNumberOfInternalNodes() {
          assertThat(this.A.numberOfInternalNodes()).isEqualTo(1);
          assertThat(this.NA.numberOfInternalNodes()).isEqualTo(1);
      }
  
      @Test
      public void testNumberOfOperands() {
          assertThat(this.A.numberOfOperands()).isEqualTo(0);
          assertThat(this.NA.numberOfOperands()).isEqualTo(0);
      }
  
      @Test
      public void testIsConstantFormula() {
          assertThat(this.A.isConstantFormula()).isFalse();
          assertThat(this.NA.isConstantFormula()).isFalse();
      }
  
      @Test
      public void testAtomicFormula() {
          assertThat(this.A.isAtomicFormula()).isTrue();
          assertThat(this.NA.isAtomicFormula()).isTrue();
      }
  
      @Test
      public void testContains() {
          assertThat(this.A.containsVariable(this.f.variable("b"))).isFalse();
          assertThat(this.A.containsVariable(this.f.variable("a"))).isTrue();
          assertThat(this.NA.containsVariable(this.f.variable("b"))).isFalse();
          assertThat(this.NA.containsVariable(this.f.variable("a"))).isTrue();
      }
  
      @Test
      public void testIsNNF() {
          assertThat(this.A.isNNF()).isTrue();
          assertThat(this.NA.isNNF()).isTrue();
      }
  
      @Test
      public void testIsDNF() {
          assertThat(this.A.isDNF()).isTrue();
          assertThat(this.NA.isDNF()).isTrue();
      }
  
      @Test
      public void testIsCNF() {
          assertThat(this.A.isCNF()).isTrue();
          assertThat(this.NA.isCNF()).isTrue();
      }
  
      @Test
      public void testPosNeg() {
          assertThat(this.A.variable() == this.A).isTrue();
          assertThat(this.NA.variable() == this.A).isTrue();
      }
  }
  