[JAVA-14174] Renamed paterns to paterns-module (#12718)

* [JAVA-14174] Renamed paterns to paterns-module

* [JAVA-14174] naming fixes

Co-authored-by: panagiotiskakos <panagiotis.kakos@libra-is.com>

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/constructorsstaticfactorymethods/UserUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.constructorsstaticfactorymethods;
+
+import com.baeldung.constructorsstaticfactorymethods.entities.User;
+import static org.assertj.core.api.Assertions.assertThat;
+import org.junit.Test;
+
+public class UserUnitTest {
+    
+    @Test
+    public void givenUserClass_whenCalledcreateWithDefaultCountry_thenCorrect() {
+        assertThat(User.createWithDefaultCountry("John", "john@domain.com")).isInstanceOf(User.class);
+    }
+    
+    @Test
+    public void givenUserIntanceCreatedWithcreateWithDefaultCountry_whenCalledgetName_thenCorrect() {
+        User user = User.createWithDefaultCountry("John", "john@domain.com");
+        assertThat(user.getName()).isEqualTo("John");
+    }
+    
+    @Test
+    public void givenUserIntanceCreatedWithcreateWithDefaultCountry_whenCalledgetEmail_thenCorrect() {
+        User user = User.createWithDefaultCountry("John", "john@domain.com");
+        assertThat(user.getEmail()).isEqualTo("john@domain.com");
+    }
+    
+    @Test
+    public void givenUserIntanceCreatedWithcreateWithDefaultCountry_whenCalledgetCountry_thenCorrect() {
+        User user = User.createWithDefaultCountry("John", "john@domain.com");
+        assertThat(user.getCountry()).isEqualTo("Argentina");
+    }
+    
+    @Test
+    public void givenUserInstanceCreatedWithcreateWithInstantiationTime_whenCalledcreateWithInstantiationTime_thenCorrect() {
+        assertThat(User.createWithLoggedInstantiationTime("John", "john@domain.com", "Argentina")).isInstanceOf(User.class);
+    }
+    
+    @Test
+    public void givenUserInstanceCreatedWithgetSingletonIntance_whenCalledgetSingletonInstance_thenCorrect() {
+        User user1 = User.getSingletonInstance("John", "john@domain.com", "Argentina");
+        User user2 = User.getSingletonInstance("John", "john@domain.com", "Argentina");
+        assertThat(user1).isEqualTo(user2);
+    }
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/creational/abstractfactory/AbstractPatternIntegrationTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.creational.abstractfactory;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class AbstractPatternIntegrationTest {
+    @Test
+    public void givenAbstractFactory_whenGettingObjects_thenSuccessful() {
+        AbstractFactory abstractFactory;
+        
+        //creating a brown toy dog
+        abstractFactory = FactoryProvider.getFactory("Toy");
+        Animal toy = (Animal) abstractFactory.create("Dog");
+        
+        abstractFactory = FactoryProvider.getFactory("Color");
+        Color color =(Color) abstractFactory.create("Brown");
+        
+        String result = "A " + toy.getType() + " with " + color.getColor() + " color " + toy.makeSound();
+        assertEquals("A Dog with brown color Barks", result);
+    }
+
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/creational/builder/BuilderPatternIntegrationTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.creational.builder;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class BuilderPatternIntegrationTest {
+    @Test
+    public void whenCreatingObjectThroughBuilder_thenObjectValid() {
+        BankAccount newAccount = new BankAccount
+          .BankAccountBuilder("Jon", "22738022275")
+          .withEmail("jon@example.com")
+          .wantNewsletter(true)
+          .build();
+        
+        assertEquals(newAccount.getName(), "Jon");
+        assertEquals(newAccount.getAccountNumber(), "22738022275");
+        assertEquals(newAccount.getEmail(), "jon@example.com");
+        assertEquals(newAccount.isNewsletter(), true);
+    }
+    
+    @Test
+    public void whenSkippingOptionalParameters_thenObjectValid() {
+        BankAccount newAccount = new BankAccount
+          .BankAccountBuilder("Jon", "22738022275")
+          .build();
+        
+        assertEquals(newAccount.getName(), "Jon");
+        assertEquals(newAccount.getAccountNumber(), "22738022275");
+        assertEquals(newAccount.getEmail(), null);
+        assertEquals(newAccount.isNewsletter(), false);
+    }
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/creational/factory/FactoryIntegrationTest.java

@@ -0,0 +1,32 @@
+package com.baeldung.creational.factory;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+public class FactoryIntegrationTest {
+
+    @Test
+    public void whenUsingFactoryForSquare_thenCorrectObjectReturned() {
+        Polygon p;
+        PolygonFactory factory = new PolygonFactory();
+        
+        //get the shape which has 4 sides
+        p = factory.getPolygon(4);
+        String result = "The shape with 4 sides is a " + p.getType();
+        
+        assertEquals("The shape with 4 sides is a Square", result);
+    }
+    
+    @Test
+    public void whenUsingFactoryForOctagon_thenCorrectObjectReturned() {
+        Polygon p;
+        PolygonFactory factory = new PolygonFactory();
+        
+        //get the shape which has 4 sides
+        p = factory.getPolygon(8);
+        String result = "The shape with 8 sides is a " + p.getType();
+        
+        assertEquals("The shape with 8 sides is a Octagon", result);
+    }
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/creational/singleton/SingletonIntegrationTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.creational.singleton;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class SingletonIntegrationTest {
+
+    @Test
+    /**
+     * Although there is absolutely no way to determine whether
+     * a class is Singleton, in this test case, we will just 
+     * check for two objects if they point to same instance or 
+     * not. We will also check for their hashcode.
+     */
+    public void whenGettingMultipleObjects_thenAllPointToSame() {
+        //first object
+        Singleton obj1 = Singleton.getInstance();
+        
+        //Second object
+        Singleton obj2 = Singleton.getInstance();
+        
+        assertTrue(obj1 == obj2);
+        assertEquals(obj1.hashCode(), obj2.hashCode());
+    }
+
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/flyweight/FlyweightUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.flyweight;
+
+import java.awt.Color;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit test for {@link VehicleFactory}.
+ * 
+ * @author Donato Rimenti
+ */
+public class FlyweightUnitTest {
+
+	/**
+	 * Checks that when the {@link VehicleFactory} is asked to provide two
+	 * vehicles of different colors, the objects returned are different.
+	 */
+	@Test
+	public void givenDifferentFlyweightObjects_whenEquals_thenFalse() {
+		Vehicle blackVehicle = VehicleFactory.createVehicle(Color.BLACK);
+		Vehicle blueVehicle = VehicleFactory.createVehicle(Color.BLUE);
+
+		Assert.assertNotNull("Object returned by the factory is null!", blackVehicle);
+		Assert.assertNotNull("Object returned by the factory is null!", blueVehicle);
+		Assert.assertNotEquals("Objects returned by the factory are equals!", blackVehicle, blueVehicle);
+	}
+
+	/**
+	 * Checks that when the {@link VehicleFactory} is asked to provide two
+	 * vehicles of the same colors, the same object is returned twice.
+	 */
+	@Test
+	public void givenSameFlyweightObjects_whenEquals_thenTrue() {
+		Vehicle blackVehicle = VehicleFactory.createVehicle(Color.BLACK);
+		Vehicle anotherBlackVehicle = VehicleFactory.createVehicle(Color.BLACK);
+
+		Assert.assertNotNull("Object returned by the factory is null!", blackVehicle);
+		Assert.assertNotNull("Object returned by the factory is null!", anotherBlackVehicle);
+		Assert.assertEquals("Objects returned by the factory are not equals!", blackVehicle, anotherBlackVehicle);
+	}
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/freebuilder/EmployeeBuilderUnitTest.java

@@ -0,0 +1,226 @@
+package com.baeldung.freebuilder;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class EmployeeBuilderUnitTest {
+
+    private static final int PIN_CODE = 223344;
+    public static final String CITY_NAME = "New York";
+    public static final int INPUT_SALARY_EUROS = 10000;
+    public static final double EUROS_TO_USD_RATIO = 0.6;
+
+    @Test
+    public void whenBuildEmployeeWithAddress_thenReturnEmployeeWithValidAddress() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setPermanent(true)
+          .setRole("developer")
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getAddress().getCity().equalsIgnoreCase(CITY_NAME));
+
+    }
+
+    @Test
+    public void whenMapSalary_thenReturnEmployeeWithSalaryInUSD() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).setPinCode(PIN_CODE).build();
+
+        long salaryInEuros = INPUT_SALARY_EUROS;
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder
+          .setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setPermanent(true)
+          .setRole("developer")
+          .setAddress(address)
+          .mapSalaryInUSD(sal -> salaryInEuros * EUROS_TO_USD_RATIO)
+          .build();
+
+        // then
+        assertTrue(employee.getAddress().getPinCode().get() == PIN_CODE);
+
+    }
+
+    @Test
+    public void whenOptionalFields_thenReturnEmployeeWithEmptyValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setPermanent(true)
+          .setRole("developer")
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getPermanent().isPresent());
+        assertTrue(employee.getPermanent().get());
+        assertFalse(employee.getDateOfJoining().isPresent());
+
+    }
+
+    @Test
+    public void whenNullableFields_thenReturnEmployeeWithNullValueForField() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .setAddress(address)
+          .build();
+
+        // then
+        assertNull(employee.getCurrentProject());
+
+    }
+
+    @Test
+    public void whenCollectionFields_thenReturnEmployeeWithValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .addAccessTokens(1221819L)
+          .addAccessTokens(1223441L, 134567L)
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getAccessTokens().size() == 3);
+
+    }
+
+    @Test
+    public void whenMapFields_thenReturnEmployeeWithValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .addAccessTokens(1221819L)
+          .addAccessTokens(1223441L, 134567L)
+          .putAssetsSerialIdMapping("Laptop", 12345L)
+          .setAddress(address)
+          .build();
+
+        // then
+        assertTrue(employee.getAssetsSerialIdMapping().size() == 1);
+
+    }
+
+    @Test
+    public void whenNestedBuilderTypes_thenReturnEmployeeWithValues() {
+
+        // when
+        Address.Builder addressBuilder = new Address.Builder();
+        Address address = addressBuilder.setCity(CITY_NAME).build();
+
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setDesignation("author")
+          .setEmail("abc@xyz.com")
+          .setSupervisorName("Admin")
+          .setPhoneNumber(4445566)
+          .setNullablePermanent(null)
+          .setDateOfJoining(Optional.empty())
+          .setRole("developer")
+          .addAccessTokens(1221819L)
+          .addAccessTokens(1223441L, 134567L)
+          .putAssetsSerialIdMapping("Laptop", 12345L)
+          .setAddress(address)
+          .mutateAddress(a -> a.setPinCode(112200))
+          .build();
+
+        // then
+        assertTrue(employee.getAssetsSerialIdMapping().size() == 1);
+
+    }
+
+    @Test()
+    public void whenPartialEmployeeWithValidEmail_thenReturnEmployeeWithEmail() {
+
+        // when
+        Employee.Builder builder = new Employee.Builder();
+
+        Employee employee = builder.setName("baeldung")
+          .setAge(10)
+          .setEmail("abc@xyz.com")
+          .buildPartial();
+
+        assertNotNull(employee.getEmail());
+    }
+
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/freebuilder/builder/EmployeeBuilderUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.freebuilder.builder;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+
+class EmployeeBuilderUnitTest {
+
+    public static final String NAME = "baeldung";
+
+    @Test
+    public void whenBuildEmployee_thenReturnValidEmployee() {
+
+        // when
+        Employee.Builder emplBuilder = new Employee.Builder();
+
+        Employee employee = emplBuilder
+          .setName(NAME)
+          .setAge(12)
+          .setDepartment("Builder Pattern")
+          .build();
+
+        //then
+        Assertions.assertTrue(employee.getName().equalsIgnoreCase(NAME));
+    }
+
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/prototype/TreePrototypeUnitTest.java

@@ -0,0 +1,68 @@
+package com.baeldung.prototype;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+import java.util.List;
+import static java.util.stream.Collectors.toList;
+
+import org.junit.jupiter.api.Test;
+
+public class TreePrototypeUnitTest {
+
+    @Test
+    public void givenAPlasticTreePrototypeWhenClonedThenCreateA_Clone() {
+        double mass = 10.0;
+        double height = 3.7;
+        Position position = new Position(3, 7);
+        Position otherPosition = new Position(4, 8);
+
+        PlasticTree plasticTree = new PlasticTree(mass, height);
+        plasticTree.setPosition(position);
+        PlasticTree anotherPlasticTree = (PlasticTree) plasticTree.copy();
+        anotherPlasticTree.setPosition(otherPosition);
+
+        assertEquals(position, plasticTree.getPosition());
+        assertEquals(otherPosition, anotherPlasticTree.getPosition());
+
+    }
+
+    @Test
+    public void givenAPineTreePrototypeWhenClonedThenCreateA_Clone() {
+        double mass = 10.0;
+        double height = 3.7;
+        Position position = new Position(3, 7);
+        Position otherPosition = new Position(4, 8);
+
+        PineTree pineTree = new PineTree(mass, height);
+        pineTree.setPosition(position);
+        PineTree anotherPineTree = (PineTree) pineTree.copy();
+        anotherPineTree.setPosition(otherPosition);
+
+        assertEquals(position, pineTree.getPosition());
+        assertEquals(otherPosition, anotherPineTree.getPosition());
+    }
+    
+    @Test
+    public void givenA_ListOfTreesWhenClonedThenCreateListOfClones() {
+        double mass = 10.0;
+        double height = 3.7;
+        Position position = new Position(3, 7);
+        Position otherPosition = new Position(4, 8);
+        
+        PlasticTree plasticTree = new PlasticTree(mass, height);
+        plasticTree.setPosition(position);
+        PineTree pineTree = new PineTree(mass, height);
+        pineTree.setPosition(otherPosition);
+        
+        List<Tree> trees = Arrays.asList(plasticTree, pineTree);
+        
+        List<Tree> treeClones = trees.stream().map(Tree::copy).collect(toList());
+        
+        Tree plasticTreeClone = treeClones.get(0);
+        
+        assertEquals(mass, plasticTreeClone.getMass());
+        assertEquals(height, plasticTreeClone.getHeight());
+        assertEquals(position, plasticTreeClone.getPosition());
+    }
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/reduceIfelse/CalculatorUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.reduceIfelse;
+
+import com.baeldung.reducingIfElse.AddCommand;
+import com.baeldung.reducingIfElse.Calculator;
+import com.baeldung.reducingIfElse.Operator;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class CalculatorUnitTest {
+
+    @Test
+    public void whenCalculateUsingStringOperator_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculate(3, 4, "add");
+        assertEquals(7, result);
+    }
+
+    @Test
+    public void whenCalculateUsingEnumOperator_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculate(3, 4, Operator.valueOf("ADD"));
+        assertEquals(7, result);
+    }
+
+    @Test
+    public void whenCalculateUsingCommand_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculate(new AddCommand(3, 7));
+        assertEquals(10, result);
+    }
+
+    @Test
+    public void whenCalculateUsingFactory_thenReturnCorrectResult() {
+        Calculator calculator = new Calculator();
+        int result = calculator.calculateUsingFactory(3, 4, "add");
+        assertEquals(7, result);
+    }
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/reduceIfelse/RuleEngineUnitTest.java

@@ -0,0 +1,23 @@
+package com.baeldung.reduceIfelse;
+
+import com.baeldung.reducingIfElse.Expression;
+import com.baeldung.reducingIfElse.Operator;
+import com.baeldung.reducingIfElse.Result;
+import com.baeldung.reducingIfElse.RuleEngine;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+public class RuleEngineUnitTest {
+
+    @Test
+    public void whenNumbersGivenToRuleEngine_thenReturnCorrectResult() {
+        Expression expression = new Expression(5, 5, Operator.ADD);
+        RuleEngine engine = new RuleEngine();
+        Result result = engine.process(expression);
+
+        assertNotNull(result);
+        assertEquals(10, result.getValue());
+    }
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/singleton/synchronization/SingletonSynchronizationIntegrationTest.java

@@ -0,0 +1,119 @@
+package com.baeldung.singleton.synchronization;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * Unit tests for the singleton synchronization package with the same name.
+ * 
+ * @author Donato Rimenti
+ *
+ */
+public class SingletonSynchronizationIntegrationTest {
+
+	/**
+	 * Size of the thread pools used.
+	 */
+	private static final int POOL_SIZE = 1_000;
+	
+	/**
+	 * Number of tasks to submit.
+	 */
+	private static final int TASKS_TO_SUBMIT = 1_000_000;
+
+	/**
+	 * Tests the thread-safety of {@link DraconianSingleton}.
+	 */
+	@Test
+	public void givenDraconianSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<DraconianSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(DraconianSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+	
+	/**
+	 * Tests the thread-safety of {@link DclSingleton}.
+	 */
+	@Test
+	public void givenDclSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<DclSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(DclSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link EarlyInitSingleton}.
+	 */
+	@Test
+	public void givenEarlyInitSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<EarlyInitSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(EarlyInitSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link InitOnDemandSingleton}.
+	 */
+	@Test
+	public void givenInitOnDemandSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<InitOnDemandSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(InitOnDemandSingleton.getInstance()));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+
+	/**
+	 * Tests the thread-safety of {@link EnumSingleton}.
+	 */
+	@Test
+	public void givenEnumSingleton_whenMultithreadInstancesEquals_thenTrue() {
+		ExecutorService executor = Executors.newFixedThreadPool(POOL_SIZE);
+		Set<EnumSingleton> resultSet = Collections.synchronizedSet(new HashSet<>());
+
+		// Submits the instantiation tasks.
+		for (int i = 0; i < TASKS_TO_SUBMIT; i++) {
+			executor.submit(() -> resultSet.add(EnumSingleton.INSTANCE));
+		}
+
+		// Since the instance of the object we inserted into the set is always
+		// the same, the size should be one.
+		Assert.assertEquals(1, resultSet.size());
+	}
+}