@Test
public void testVisitorId_restore() {

    Tracker tracker = new Tracker(mMatomo, mTrackerBuilder);
    assertThat(tracker.getVisitorId(), is(notNullValue()));
    String visitorId = tracker.getVisitorId();
    tracker = new Tracker(mMatomo, mTrackerBuilder);
    assertThat(tracker.getVisitorId(), is(visitorId));
}