Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
prō-testor, ātus, 1, v. dep. a. (act. collat. form prōtesto, āre, acc. to Prisc. p. 799), to declare in public, to bear witness, testify, protest (post-Aug.): praedico, protestor, non ego parricidium faciam, Quint. Decl. 4, 21: quae mihi conscius sum, protestabor, Front. Nep. Am. 2 Mai: floris species florem rerum protestatur, Macr. S. 1, 17 fin.: mulier magno fidem praesidis protestata clamore, App. M. 10, p. 252; Vulg. Act. 20, 23; Just. Inst. prooem. 1.
With object-clause: quippe protestantur, pietatis gratiā id se facere, Dig. 11, 7, 14, § 8.