What is the test for a joint tenant's claim to all of the property in the absence of a spouse who has been found guilty of murder?

" 'The theory underlying those decisions which justify the result of the heirs of the murdered joint tenant taking all (not merely one-half) of the property is that, by reason of the murder, the murdered joint tenant is thereby prevented from ever securing title to the whole by survivorship. However, it is entirely a matter of speculation as to which joint tenant would have outlived the other, in the event the murder had not been committed, or that a severance would not have taken place during the lifetime of both joint tenants as a result of alienation by either, partition, or divorce. Therefore it seems that the result reached [by these cases allowing all of the property to go to the victim's estate come] very close to working a corruption of blood, or a forfeiture of estate, as to one who has been guilty of crime....' [Citation.]" (Johansen v. Pelton, supra, at p. [135 Cal.App.3d 691] 633, 87 Cal.Rptr. 784.)