What is considered moot and what is the test for dismissing an appeal?

" ' "[T]he duty of this court, as of every other judicial tribunal, is to decide actual controversies by a judgment which can be carried into effect, and not to give opinions upon moot questions or abstract propositions, or to declare principles or rules of law which cannot affect the matter in issue in the case before it." ' . . . 'It necessarily follows that when, pending an appeal from the judgment of a lower court, and without any fault of the defendant, an event occurs which renders it impossible for this court, if it should decide the case in favor of plaintiff, to grant him any effectual relief whatever, the court will not proceed to a formal judgment, but will dismiss the appeal.' [Citations.]" (Eye Dog Foundation v. State Board of Guide Dogs for the Blind (1967) 67 Cal.2d 536, 541.) Stated more succinctly: " 'A case is moot when the decision of the reviewing court "can have no practical impact or provide the parties effectual relief. [Citation.]" [Citation.] "When no effectual relief can be granted, an appeal is moot and will be dismissed." [Citations.]' " (Steiner v. Superior Court (2013) 220 Cal.App.4th 1479, 1485.)