。
The court ruled that the will was valid.
Literal
Court [topic-は] will [subject-が] valid [quotative-である-との] judgment [object-を] handed-down
The との is a compound marker: と (quotative) + の (adnominal) = 'the verdict that says X'. Literally '(handed down) a verdict of [the will is valid]'. である inside the quoted clause gives it the formal written copula. 遺言状 = written will (a legal document).