@Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        final Activity activity = (Activity) o;
        return Objects.equals(caller, activity.caller) && Objects.equals(message, activity.message);
    }
@Test
    public void testEquals() throws Exception {
        EqualsVerifier.forClass(Activity.class)
            .suppress(Warning.NONFINAL_FIELDS)
            .verify();
    }