### Question:
BackButtonHelper { public void clear(ViewController child) { if (!child.options.topBar.buttons.back.hasValue()) { child.options.topBar.buttons.back.visible = new Bool(false); } }  void addToPushedChild(ViewController child); void clear(ViewController child);  }### Answer:
@Test public void clear() { child1.options.topBar.buttons.back.visible = new Bool(true); uut.clear(child1); assertThat(child1.options.topBar.buttons.back.visible.get()).isFalse(); }