public class Person {

    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {

        if (age < 0 ) {
            throw new IllegalArgumentException("age is invalid");
        }
        this.age = age;
    }
}

    @Test
    public void shouldGetExceptionWhenAgeLessThan0() {
        Person person = new Person();
        try {
        person.setAge(-1);
            fail("should get IllegalArgumentException");
        } catch (IllegalArgumentException ex) {
            assertThat(ex.getMessage(),containsString("age is invalid"));
        }

    }