"Sworn testimony" refers to a statement or evidence given by a person under oath, meaning they promise to tell the truth before providing their information. Full definition
He's now requesting a public hearing on the matter with sworn testimony from witnesses. (michaelbenjamin2012.com)
We actively assist by providing care for the animals, and if necessary, sworn testimony on the animal's condition to be used in court. (animalwelfaresociety.org)
In other words, there's no way to be certain, save for getting sworn testimony by government officials. (law.stackexchange.com)