 In practical terms testamentary trusts tend to be driven more by the needs of the beneficiaries (particularly infant beneficiaries) than by tax considerations, which are the usual considerations in "inter vivos" trusts.If a testamentary trust fails, the property usually will be held on resulting trusts for the testator's residuary estate.Some famous English trust law cases were on behalf of the residuary legatees under a will seeking to have testamentary trusts declared void so as to inherit the trust property.