### Question:
Phial { public static void removeSaver(Saver saver) { SAVERS.remove(saver); }  static void setKey(String key, String value); static void setKey(@NonNull String key, @Nullable Object value); static void removeKey(String key); static Category category(String name); static void removeCategory(String name); static void addSaver(Saver saver); static void removeSaver(Saver saver);  }### Answer:
@Test public void removeSaver() { savers.forEach(Phial::removeSaver); Phial.setKey("key", "value"); Phial.removeKey("key"); Phial.category("category").setKey("key", "value"); Phial.category("category").removeKey("key"); savers.forEach(Mockito::verifyZeroInteractions); }