[BAEL-3077] Add examples for mapstruct with multiple source objects (#7724)

* [BAEL-3077] Add examples for mapstruct with multiple source objects

* [BAEL-3077] Add unit tests for mappers added by examples

mapstruct/src/test/java/com/baeldung/mapper/DeliveryAddressMapperUnitTest.java

@@ -0,0 +1,64 @@
+package com.baeldung.mapper;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
+
+import org.junit.Test;
+import org.mapstruct.factory.Mappers;
+
+import com.baeldung.entity.Address;
+import com.baeldung.entity.Customer;
+import com.baeldung.entity.DeliveryAddress;
+
+public class DeliveryAddressMapperUnitTest {
+
+    private DeliveryAddressMapper deliveryAddressMapper = Mappers.getMapper(DeliveryAddressMapper.class);
+
+    @Test
+    public void testGivenCustomerAndAddress_mapsToDeliveryAddress() {
+
+        // given
+        Customer customer = new Customer().setFirstName("Max")
+            .setLastName("Powers");
+
+        Address homeAddress = new Address().setStreet("123 Some Street")
+            .setCounty("Nevada")
+            .setPostalcode("89123");
+
+        // when
+        DeliveryAddress deliveryAddress = deliveryAddressMapper.from(customer, homeAddress);
+
+        // then
+        assertEquals(deliveryAddress.getForename(), customer.getFirstName());
+        assertEquals(deliveryAddress.getSurname(), customer.getLastName());
+        assertEquals(deliveryAddress.getStreet(), homeAddress.getStreet());
+        assertEquals(deliveryAddress.getCounty(), homeAddress.getCounty());
+        assertEquals(deliveryAddress.getPostalcode(), homeAddress.getPostalcode());
+    }
+
+    @Test
+    public void testGivenDeliveryAddressAndSomeOtherAddress_updatesDeliveryAddress() {
+
+        // given
+        Customer customer = new Customer().setFirstName("Max")
+            .setLastName("Powers");
+
+        DeliveryAddress deliveryAddress = new DeliveryAddress().setStreet("123 Some Street")
+            .setCounty("Nevada")
+            .setPostalcode("89123");
+
+        Address otherAddress = new Address().setStreet("456 Some other street")
+            .setCounty("Arizona")
+            .setPostalcode("12345");
+
+        // when
+        DeliveryAddress updatedDeliveryAddress = deliveryAddressMapper.updateAddress(deliveryAddress, otherAddress);
+
+        // then
+        assertSame(deliveryAddress, updatedDeliveryAddress);
+
+        assertEquals(deliveryAddress.getStreet(), otherAddress.getStreet());
+        assertEquals(deliveryAddress.getCounty(), otherAddress.getCounty());
+        assertEquals(deliveryAddress.getPostalcode(), otherAddress.getPostalcode());
+    }
+}