Add remaining examples

immutables/src/test/java/com/baeldung/immutable/default_/ImmutablePersonDefaultTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.immutable.default_;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ImmutablePersonDefaultTest {
+
+    @Test
+    public void whenInstantiating_shouldUseDefaultValue() throws Exception {
+
+        final com.baeldung.immutable.default_.ImmutablePerson john = com.baeldung.immutable.default_.ImmutablePerson.builder().name("John").build();
+
+        assertThat(john.getAge()).isEqualTo(42);
+
+    }
+}