@Test
public void peekRouter() {

  assertThat(routerNavigator.peekRouter()).isNull();
  routerNavigator.pushRetainedState(TestState.STATE_1, attachTransitionOne, detachTransitionOne);
  assertThat(routerNavigator.peekRouter()).isEqualTo(routerOne);
  routerNavigator.popState();
  assertThat(routerNavigator.peekRouter()).isNull();
}