In the case of Yiatchos v. Yiatchos, Executrix, et al., 1963, the U.S Supreme Court was tasked with determining whether a joint bank account could be considered as a testamentary substitute under Washington state law. The dispute arose after Mr. Andrew Yiatchos died without leaving a will and his sister claimed that she was entitled to funds in two joint savings accounts they held together because he had intended for her to have them upon his death. However, other family members contested this claim arguing that these funds should be part of the deceased's estate and divided among all heirs according to intestacy laws. The court ruled in favor of Mr.Yiatchos' sister stating that under Washington law at the time, such jointly owned accounts were indeed treated as testamentary substitutes if it can be proven there was an intention by one party for another party to receive those assets upon their death - which she successfully did through evidence presented during trial proceedings.

In the dissenting opinion for Yiatchos v. Yiatchos, Executrix, et al., Justice Harlan disagreed with the majority's interpretation of Washington state law and its application to federal savings bonds. He argued that it was not clear whether Washington would have considered these bonds as community property or separate property under its laws at the time they were purchased. Furthermore, he believed that even if they were deemed community property, it did not necessarily mean that upon death of one spouse half of each bond automatically belonged to the surviving spouse. Instead, he suggested this issue should be decided by looking at who had possession and control over them during their lifetime - a fact-specific inquiry which had been ignored in this case.