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.knowledgecompilation.bdds;
  
  import static org.assertj.core.api.Assertions.assertThat;
  
  import org.junit.jupiter.api.BeforeEach;
  import org.junit.jupiter.api.Test;
  import org.logicng.formulas.Formula;
  import org.logicng.formulas.FormulaFactory;
  import org.logicng.formulas.Variable;
  import org.logicng.io.parsers.ParserException;
  import org.logicng.knowledgecompilation.bdds.jbuddy.BDDKernel;
  
  import java.util.List;
  
  /**
   * Unit tests for the BDD construction methods
   * @version 2.4.0
   * @since 2.4.0
   */
  public class BDDConstructionTests {
  
      FormulaFactory f;
      List<Variable> variables;
      BDDKernel kernel;
      Formula initFormula;
      Formula secondFormula;
      BDD initBdd;
      BDD secondBdd;
  
      @BeforeEach
      public void init() throws ParserException {
          this.f = new FormulaFactory();
          this.variables = this.f.variables("a", "b", "c", "d", "e", "f", "g");
          this.kernel = new BDDKernel(this.f, this.variables, 1000, 10000);
          this.initFormula = this.f.parse("(a & b) => (c | d & ~e)");
          this.secondFormula = this.f.parse("(g & f) <=> (c | ~a | ~d)");
          this.initBdd = BDDFactory.build(this.initFormula, this.kernel);
          this.secondBdd = BDDFactory.build(this.secondFormula, this.kernel);
      }
  
      @Test
      public void testNegation() {
          final BDD negation = this.initBdd.negate();
          final BDD expected = BDDFactory.build(this.initFormula.negate(), this.kernel);
          assertThat(negation).isEqualTo(expected);
      }
  
      @Test
      public void testImplies() {
          final BDD implication = this.initBdd.implies(this.secondBdd);
          final BDD expected = BDDFactory.build(this.f.implication(this.initFormula, this.secondFormula), this.kernel);
          assertThat(implication).isEqualTo(expected);
      }
  
      @Test
      public void testIsImplied() {
          final BDD implication = this.initBdd.impliedBy(this.secondBdd);
          final BDD expected = BDDFactory.build(this.f.implication(this.secondFormula, this.initFormula), this.kernel);
          assertThat(implication).isEqualTo(expected);
      }
  
      @Test
      public void testEquivalence() {
          final BDD equivalence = this.initBdd.equivalence(this.secondBdd);
          final BDD expected = BDDFactory.build(this.f.equivalence(this.secondFormula, this.initFormula), this.kernel);
          assertThat(equivalence).isEqualTo(expected);
      }
  
      @Test
      public void testAnd() {
          final BDD and = this.initBdd.and(this.secondBdd);
          final BDD expected = BDDFactory.build(this.f.and(this.secondFormula, this.initFormula), this.kernel);
          assertThat(and).isEqualTo(expected);
      }
  
      @Test
      public void testOr() {
          final BDD or = this.initBdd.or(this.secondBdd);
          final BDD expected = BDDFactory.build(this.f.or(this.secondFormula, this.initFormula), this.kernel);
          assertThat(or).isEqualTo(expected);
      }
  }
  