[BAEL-5976]: Extract Values using AssertJ in Java (#13105)

JIRA: https://jira.baeldung.com/browse/BAEL-5976

testing-modules/assertion-libraries/src/main/java/com/baeldung/assertj/extracting/Address.java

@@ -0,0 +1,25 @@
+package com.baeldung.assertj.extracting;
+
+class Address {
+    private String street;
+    private String city;
+    private ZipCode zipCode;
+
+    Address(String street, String city, ZipCode zipCode) {
+        this.street = street;
+        this.city = city;
+        this.zipCode = zipCode;
+    }
+
+    public String getStreet() {
+        return street;
+    }
+
+    public String getCity() {
+        return city;
+    }
+
+    public ZipCode getZipCode() {
+        return zipCode;
+    }
+}

testing-modules/assertion-libraries/src/main/java/com/baeldung/assertj/extracting/Person.java

@@ -0,0 +1,25 @@
+package com.baeldung.assertj.extracting;
+
+class Person {
+    private String firstName;
+    private String lastName;
+    private Address address;
+
+    Person(String firstName, String lastName, Address address) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+        this.address = address;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+}

testing-modules/assertion-libraries/src/main/java/com/baeldung/assertj/extracting/ZipCode.java

@@ -0,0 +1,13 @@
+package com.baeldung.assertj.extracting;
+
+class ZipCode {
+    private long zipcode;
+
+    ZipCode(long zipcode) {
+        this.zipcode = zipcode;
+    }
+
+    public long getZipcode() {
+        return zipcode;
+    }
+}

testing-modules/assertion-libraries/src/test/java/com/baeldung/assertj/extracting/AssertJExtractingUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.assertj.extracting;
+
+import org.assertj.core.api.InstanceOfAssertFactories;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.as;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class AssertJExtractingUnitTest {
+    static final List<Address> RESTRICTED_ADDRESSES = new ArrayList<>();
+
+    @Test
+    void whenUsingRegularAssertionFlow_thenCorrect() {
+
+        // Given
+        Person person = new Person("aName", "aLastName", new Address("aStreet", "aCity", new ZipCode(90210)));
+
+        // Then
+        Address address = person.getAddress();
+        assertThat(address).isNotNull()
+          .isNotIn(RESTRICTED_ADDRESSES);
+        ZipCode zipCode = address.getZipCode();
+        assertThat(zipCode).isNotNull();
+        assertThat(zipCode.getZipcode()).isBetween(1000L, 100_000L);
+    }
+
+    @Test
+    void whenUsingExtractingAssertionFlow_thenCorrect() {
+
+        // Given
+        Person person = new Person("aName", "aLastName", new Address("aStreet", "aCity", new ZipCode(90210)));
+
+        // Then
+        assertThat(person)
+          .extracting(Person::getAddress)
+          .isNotNull()
+          .isNotIn(RESTRICTED_ADDRESSES)
+          .extracting(Address::getZipCode)
+          .isNotNull()
+          .extracting(ZipCode::getZipcode, as(InstanceOfAssertFactories.LONG))
+          .isBetween(1_000L, 100_000L);
+    }
+}