package com.baeldung.immutable; import org.junit.Test; import static org.assertj.core.api.Assertions.assertThat; public class ImmutablePersonTest { @Test public void whenModifying_shouldCreateNewInstance() throws Exception { final com.baeldung.immutable.ImmutablePerson john = com.baeldung.immutable.ImmutablePerson.builder() .age(42) .name("John") .build(); final com.baeldung.immutable.ImmutablePerson john43 = john.withAge(43); assertThat(john) .isNotSameAs(john43); assertThat(john.getAge()) .isEqualTo(42); } }