New unit test format

patterns/design-patterns-2/README.md

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+### Relevant Articles
+
+- [The Mediator Pattern in Java](https://www.baeldung.com/java-mediator-pattern)
+- [Introduction to the Null Object Pattern](https://www.baeldung.com/java-null-object-pattern)
+- [Avoid Check for Null Statement in Java](https://www.baeldung.com/java-avoid-null-check)

patterns/design-patterns-2/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>design-patterns-2</artifactId>
+    <version>1.0</version>
+    <name>design-patterns-2</name>
+	<packaging>jar</packaging>
+	
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>patterns</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+        <relativePath>..</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.jetbrains</groupId>
+            <artifactId>annotations</artifactId>
+            <version>${intellij.annotations.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+   		<dependency>
+            <groupId>org.inferred</groupId>
+            <artifactId>freebuilder</artifactId>
+            <version>${freebuilder.version}</version>
+            <optional>true</optional>
+        </dependency>
+        <dependency>
+            <groupId>com.google.code.findbugs</groupId>
+            <artifactId>jsr305</artifactId>
+            <version>${javax.annotations.version}</version>
+        </dependency>
+    </dependencies>
+    
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
+        <intellij.annotations.version>16.0.2</intellij.annotations.version>
+        <assertj.version>3.12.2</assertj.version>
+        <freebuilder.version>2.4.1</freebuilder.version>
+        <javax.annotations.version>3.0.2</javax.annotations.version>
+    </properties>
+</project>

patterns/design-patterns-2/src/main/java/com/baeldung/freebuilder/Address.java

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+package com.baeldung.freebuilder;
+
+import org.inferred.freebuilder.FreeBuilder;
+
+import java.util.Optional;
+
+@FreeBuilder
+public interface Address {
+
+    Optional<String> getAddressLine1();
+
+    Optional<String> getAddressLine2();
+
+    Optional<String> getAddressLine3();
+
+    String getCity();
+
+    Optional<String> getState();
+
+    Optional<Long> getPinCode();
+
+    class Builder extends Address_Builder {
+
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/freebuilder/Employee.java

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+package com.baeldung.freebuilder;
+
+import org.inferred.freebuilder.FreeBuilder;
+
+import javax.annotation.Nullable;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+@FreeBuilder
+public interface Employee {
+
+    String getName();
+
+    int getAge();
+
+    String getDepartment();
+
+    String getRole();
+
+    String getSupervisorName();
+
+    String getDesignation();
+
+    String getEmail();
+
+    long getPhoneNumber();
+
+    Optional<Boolean> getPermanent();
+
+    Optional<String> getDateOfJoining();
+
+    @Nullable
+    String getCurrentProject();
+
+    Address getAddress();
+
+    List<Long> getAccessTokens();
+
+    Map<String, Long> getAssetsSerialIdMapping();
+
+    Optional<Double> getSalaryInUSD();
+
+
+    class Builder extends Employee_Builder {
+
+        public Builder() {
+            // setting default value for department
+            setDepartment("Builder Pattern");
+        }
+
+        @Override
+        public Builder setEmail(String email) {
+            if (checkValidEmail(email))
+                return super.setEmail(email);
+            else
+                throw new IllegalArgumentException("Invalid email");
+
+        }
+
+        private boolean checkValidEmail(String email) {
+            return email.contains("@");
+        }
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/freebuilder/builder/Employee.java

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+package com.baeldung.freebuilder.builder;
+
+public class Employee {
+
+    private final String name;
+    private final int age;
+    private final String department;
+
+    private Employee(String name, int age, String department) {
+        this.name = name;
+        this.age = age;
+        this.department = department;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getAge() {
+        return age;
+    }
+
+    public String getDepartment() {
+        return department;
+    }
+
+    public static class Builder {
+
+        private String name;
+        private int age;
+        private String department;
+
+        public Builder setName(String name) {
+            this.name = name;
+            return this;
+        }
+
+        public Builder setAge(int age) {
+            this.age = age;
+            return this;
+        }
+
+        public Builder setDepartment(String department) {
+            this.department = department;
+            return this;
+        }
+
+        public Employee build() {
+            return new Employee(name, age, department);
+        }
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/Button.java

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+package com.baeldung.mediator;
+
+public class Button {
+    private Mediator mediator;
+
+    public void setMediator(Mediator mediator) {
+        this.mediator = mediator;
+    }
+
+    public void press() {
+        this.mediator.press();
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/Fan.java

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+package com.baeldung.mediator;
+
+public class Fan {
+    private Mediator mediator;
+    private boolean isOn = false;
+
+    public void setMediator(Mediator mediator) {
+        this.mediator = mediator;
+    }
+
+    public boolean isOn() {
+        return isOn;
+    }
+
+    public void turnOn() {
+        this.mediator.start();
+        isOn = true;
+    }
+
+    public void turnOff() {
+        isOn = false;
+        this.mediator.stop();
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/Mediator.java

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+package com.baeldung.mediator;
+
+public class Mediator {
+    private Button button;
+    private Fan fan;
+    private PowerSupplier powerSupplier;
+
+    public void setButton(Button button) {
+        this.button = button;
+        this.button.setMediator(this);
+    }
+
+    public void setFan(Fan fan) {
+        this.fan = fan;
+        this.fan.setMediator(this);
+    }
+
+    public void setPowerSupplier(PowerSupplier powerSupplier) {
+        this.powerSupplier = powerSupplier;
+    }
+
+    public void press() {
+        if (fan.isOn()) {
+            fan.turnOff();
+        } else {
+            fan.turnOn();
+        }
+    }
+
+    public void start() {
+        powerSupplier.turnOn();
+    }
+
+    public void stop() {
+        powerSupplier.turnOff();
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/PowerSupplier.java

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+package com.baeldung.mediator;
+
+public class PowerSupplier {
+    public void turnOn() {
+        // implementation
+    }
+
+    public void turnOff() {
+        // implementation
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/memento/TextEditor.java

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+package com.baeldung.memento;
+
+public class TextEditor {
+
+    private TextWindow textWindow;
+    private TextWindowState savedTextWindow;
+
+    public TextEditor(TextWindow textWindow) {
+        this.textWindow = textWindow;
+    }
+
+    public void write(String text) {
+        textWindow.addText(text);
+    }
+
+    public String print() {
+        return textWindow.getCurrentText();
+    }
+
+    public void hitSave() {
+        savedTextWindow = textWindow.save();
+    }
+
+    public void hitUndo() {
+        textWindow.restore(savedTextWindow);
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/memento/TextWindow.java

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+package com.baeldung.memento;
+
+public class TextWindow {
+
+    private StringBuilder currentText;
+
+    public TextWindow() {
+        this.currentText = new StringBuilder();
+    }
+
+    public String getCurrentText() {
+        return currentText.toString();
+    }
+
+    public void addText(String text) {
+        currentText.append(text);
+    }
+
+    public TextWindowState save() {
+        return new TextWindowState(currentText.toString());
+    }
+
+    public void restore(TextWindowState save) {
+        currentText = new StringBuilder(save.getText());
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/memento/TextWindowState.java

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+package com.baeldung.memento;
+
+public class TextWindowState {
+
+    private String text;
+
+    public TextWindowState(String text) {
+        this.text = text;
+    }
+
+    public String getText() {
+        return text;
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/JmsRouter.java

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+package com.baeldung.nullobject;
+
+public class JmsRouter implements Router {
+
+    @Override
+    public void route(Message msg) {
+        System.out.println("Routing to a JMS queue. Msg: " + msg);
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/Message.java

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+package com.baeldung.nullobject;
+
+public class Message {
+
+    private String body;
+
+    private String priority;
+
+    public Message(String body, String priority) {
+        this.body = body;
+        this.priority = priority;
+    }
+
+    public String getPriority() {
+        return priority;
+    }
+
+    @Override
+    public String toString() {
+        return "{body='" + body + '\'' +
+                ", priority='" + priority + '\'' +
+                '}';
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/NullRouter.java

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+package com.baeldung.nullobject;
+
+public class NullRouter implements Router {
+
+    @Override
+    public void route(Message msg) {
+        // do nothing
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/Router.java

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+package com.baeldung.nullobject;
+
+public interface Router {
+
+    void route(Message msg);
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/RouterFactory.java

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+package com.baeldung.nullobject;
+
+public class RouterFactory {
+
+    public static Router getRouterForMessage(Message msg) {
+
+        if (msg.getPriority() == null) {
+            return new NullRouter();
+        }
+
+        switch (msg.getPriority()) {
+            case "high":
+                return new SmsRouter();
+
+            case "medium":
+                return new JmsRouter();
+
+            default:
+                return new NullRouter();
+        }
+
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/RoutingHandler.java

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+package com.baeldung.nullobject;
+
+import java.util.Arrays;
+import java.util.List;
+
+public class RoutingHandler {
+
+    public void handle(Iterable<Message> messages){
+        for (Message msg : messages) {
+            Router router = RouterFactory.getRouterForMessage(msg);
+            router.route(msg);
+        }
+    }
+
+    public static void main(String[] args) {
+        Message highPriorityMsg = new Message("Alert!", "high");
+        Message mediumPriorityMsg = new Message("Warning!", "medium");
+        Message lowPriorityMsg = new Message("Take a look!", "low");
+        Message nullPriorityMsg = new Message("Take a look!", null);
+
+        List<Message> messages = Arrays.asList(highPriorityMsg,
+                mediumPriorityMsg,
+                lowPriorityMsg,
+                nullPriorityMsg);
+
+        RoutingHandler routingHandler = new RoutingHandler();
+        routingHandler.handle(messages);
+
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nullobject/SmsRouter.java

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+package com.baeldung.nullobject;
+
+public class SmsRouter implements Router {
+
+    @Override
+    public void route(Message msg) {
+        System.out.println("Routing to a SMS gateway. Msg: " + msg);
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/APIContracts.java

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+package com.baeldung.nulls;
+
+public class APIContracts {
+
+    /**
+     * Prints the value of {@code param} if not null. Prints {@code null} otherwise.
+     *
+     * @param param
+     */
+    public void print(Object param) {
+        System.out.println("Printing " + param);
+    }
+
+    /**
+     * @return non null result
+     * @throws Exception - if result is null
+     */
+    public Object process() throws Exception {
+        Object result = doSomething();
+        if (result == null) {
+            throw new Exception("Processing fail. Got a null response");
+        } else {
+            return result;
+        }
+    }
+
+    private Object doSomething() {
+        return null;
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/Assertions.java

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+package com.baeldung.nulls;
+
+public class Assertions {
+    
+    public void accept(Object param){
+        assert param != null;
+        
+        doSomething(param);
+    }
+
+    private void doSomething(Object param) {
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/EmptyCollections.java

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+package com.baeldung.nulls;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class EmptyCollections {
+
+    public List<String> names() {
+        if (userExist()) {
+            return Stream.of(readName()).collect(Collectors.toList());
+        } else {
+            return Collections.emptyList();
+        }
+    }
+
+    private boolean userExist() {
+        return false;
+    }
+
+    private String readName() {
+        return "test";
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/FindBugsAnnotations.java

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+package com.baeldung.nulls;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+
+public class FindBugsAnnotations {
+
+    public void accept(@NotNull Object param) {
+        System.out.println(param.toString());
+    }
+
+    public void print(@Nullable Object param) {
+        System.out.println("Printing " + param);
+    }
+
+    @NotNull
+    public Object process() throws Exception {
+        Object result = doSomething();
+        if (result == null) {
+            throw new Exception("Processing fail. Got a null response");
+        } else {
+            return result;
+        }
+    }
+
+    private Object doSomething() {
+        return null;
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/Preconditions.java

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+package com.baeldung.nulls;
+
+public class Preconditions {
+
+    public void goodAccept(String one, String two, String three) {
+        if (one == null || two == null || three == null) {
+            throw new IllegalArgumentException();
+        }
+
+        process(one);
+        process(two);
+        process(three);
+    }
+
+    public void badAccept(String one, String two, String three) {
+        if (one == null) {
+            throw new IllegalArgumentException();
+        } else {
+            process(one);
+        }
+
+        if (two == null) {
+            throw new IllegalArgumentException();
+        } else {
+            process(two);
+        }
+
+        if (three == null) {
+            throw new IllegalArgumentException();
+        } else {
+            process(three);
+        }
+
+    }
+
+    private void process(String one) {
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/PrimitivesAndWrapper.java

@@ -0,0 +1,21 @@
+package com.baeldung.nulls;
+
+public class PrimitivesAndWrapper {
+
+    public static int primitiveSum(int a, int b) {
+        return a + b;
+    }
+
+    public static Integer wrapperSum(Integer a, Integer b) {
+        return a + b;
+    }
+
+    public static Integer goodSum(Integer a, Integer b) {
+        if (a != null && b != null) {
+            return a + b;
+        } else {
+            throw new IllegalArgumentException();
+        }
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingLombok.java

@@ -0,0 +1,10 @@
+package com.baeldung.nulls;
+
+import lombok.NonNull;
+
+public class UsingLombok {
+
+    public void accept(@NonNull Object param){
+        System.out.println(param);
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingObjects.java

@@ -0,0 +1,11 @@
+package com.baeldung.nulls;
+
+import java.util.Objects;
+
+public class UsingObjects {
+
+    public void accept(Object param) {
+        Objects.requireNonNull(param);
+        // doSomething()
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingOptional.java

@@ -0,0 +1,23 @@
+package com.baeldung.nulls;
+
+import java.util.Optional;
+
+public class UsingOptional {
+
+    public Optional<Object> process(boolean processed) {
+
+        String response = doSomething(processed);
+
+        return Optional.ofNullable(response);
+    }
+
+    private String doSomething(boolean processed) {
+
+        if (processed) {
+            return "passed";
+        } else {
+            return null;
+        }
+    }
+
+}

patterns/design-patterns-2/src/main/java/com/baeldung/nulls/UsingStringUtils.java

@@ -0,0 +1,22 @@
+package com.baeldung.nulls;
+
+import org.apache.commons.lang3.StringUtils;
+
+public class UsingStringUtils {
+
+    public void accept(String param) {
+        if (StringUtils.isNotEmpty(param)) {
+            System.out.println(param);
+        } else {
+            throw new IllegalArgumentException();
+        }
+    }
+
+    public void acceptOnlyNonBlank(String param) {
+        if (StringUtils.isNotBlank(param)) {
+            System.out.println(param);
+        } else {
+            throw new IllegalArgumentException();
+        }
+    }
+}

patterns/design-patterns-2/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/design-patterns-2/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/design-patterns-2/src/test/java/com/baeldung/mediator/MediatorIntegrationTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.mediator;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class MediatorIntegrationTest {
+
+    private Button button;
+    private Fan fan;
+
+    @Before
+    public void setUp() {
+        this.button = new Button();
+        this.fan = new Fan();
+        PowerSupplier powerSupplier = new PowerSupplier();
+        Mediator mediator = new Mediator();
+
+        mediator.setButton(this.button);
+        mediator.setFan(fan);
+        mediator.setPowerSupplier(powerSupplier);
+    }
+
+    @Test
+    public void givenTurnedOffFan_whenPressingButtonTwice_fanShouldTurnOnAndOff() {
+        assertFalse(fan.isOn());
+
+        button.press();
+        assertTrue(fan.isOn());
+
+        button.press();
+        assertFalse(fan.isOn());
+    }
+}

patterns/design-patterns-2/src/test/java/com/baeldung/memento/TextEditorUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.memento;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class TextEditorUnitTest {
+
+    @Test
+    void givenTextEditor_whenAddTextSaveAddMoreAndUndo_thenSavecStateRestored() {
+        TextEditor textEditor = new TextEditor(new TextWindow());
+        textEditor.write("The Memento Design Pattern\n");
+        textEditor.write("How to implement it in Java?\n");
+        textEditor.hitSave();
+        textEditor.write("Buy milk and eggs before coming home\n");
+        textEditor.hitUndo();
+
+        assertThat(textEditor.print()).isEqualTo("The Memento Design Pattern\nHow to implement it in Java?\n");
+    }
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/PrimitivesAndWrapperUnitTest.java

@@ -0,0 +1,35 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class PrimitivesAndWrapperUnitTest {
+
+    @Test
+    public void givenBothArgsNonNull_whenCallingWrapperSum_thenReturnSum() {
+
+        Integer sum = PrimitivesAndWrapper.wrapperSum(0, 0);
+
+        assertEquals(0, sum.intValue());
+    }
+
+    @Test()
+    public void givenOneArgIsNull_whenCallingWrapperSum_thenThrowNullPointerException() {
+        assertThrows(NullPointerException.class, () -> PrimitivesAndWrapper.wrapperSum(null, 2));
+    }
+
+    @Test()
+    public void givenBothArgsNull_whenCallingWrapperSum_thenThrowNullPointerException() {
+        assertThrows(NullPointerException.class, () -> PrimitivesAndWrapper.wrapperSum(null, null));
+    }
+
+    @Test()
+    public void givenOneArgNull_whenCallingGoodSum_thenThrowIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> PrimitivesAndWrapper.goodSum(null, 2));
+    }
+
+
+
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingLombokUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class UsingLombokUnitTest {
+
+    private UsingLombok classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingLombok();
+    }
+
+    @Test
+    public void whenNullArg_thenThrowNullPointerException() {
+
+        assertThrows(NullPointerException.class, () -> classUnderTest.accept(null));
+
+    }
+
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingObjectsUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class UsingObjectsUnitTest {
+
+    private UsingObjects classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingObjects();
+    }
+
+    @Test
+    public void whenArgIsNull_thenThrowException() {
+
+        assertThrows(NullPointerException.class, () -> classUnderTest.accept(null));
+    }
+
+    @Test
+    public void whenArgIsNonNull_thenDoesNotThrowException() {
+
+        assertDoesNotThrow(() -> classUnderTest.accept("test    "));
+    }
+
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingOptionalUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+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.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class UsingOptionalUnitTest {
+
+    private UsingOptional classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingOptional();
+    }
+
+    @Test
+    public void whenArgIsFalse_thenReturnEmptyResponse() {
+
+        Optional<Object> result = classUnderTest.process(false);
+
+        assertFalse(result.isPresent());
+    }
+
+    @Test
+    public void whenArgIsTrue_thenReturnValidResponse() {
+
+        Optional<Object> result = classUnderTest.process(true);
+
+        assertTrue(result.isPresent());
+    }
+
+    @Test
+    public void whenArgIsFalse_thenChainResponseAndThrowException() {
+
+        assertThrows(Exception.class, () -> classUnderTest.process(false).orElseThrow(() -> new Exception()));
+    }
+}

patterns/design-patterns-2/src/test/java/com/baeldung/nulls/UsingStringUtilsUnitTest.java

@@ -0,0 +1,42 @@
+package com.baeldung.nulls;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class UsingStringUtilsUnitTest {
+
+    private UsingStringUtils classUnderTest;
+
+    @BeforeEach
+    public void setup() {
+        classUnderTest = new UsingStringUtils();
+    }
+
+    @Test
+    public void givenArgIsNull_whenCallingAccept_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.accept(null));
+    }
+
+    @Test
+    public void givenArgIsEmpty_whenCallingAccept_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.accept(""));
+    }
+
+    @Test
+    public void givenArgIsNull_whenCallingAcceptOnlyNonBlank_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.acceptOnlyNonBlank(null));
+    }
+
+    @Test
+    public void givenArgIsEmpty_whenCallingAcceptOnlyNonBlank_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.acceptOnlyNonBlank(""));
+    }
+
+    @Test
+    public void givenArgIsBlank_whenCallingAcceptOnlyNonBlank_throwIllegalArgumentException() {
+        assertThrows(IllegalArgumentException.class, () -> classUnderTest.acceptOnlyNonBlank(" "));
+    }
+
+}