The word according to the dictionary

See also: testőr

English

testor

1949, John Dover Wilson (compiler), Life in Shakespeare's England. A Book of Elizabethan Prose, Cambridge at the University Press. 1st ed. 1911, 2nd ed. 1913, 8th reprint. In Glossary and Notes

From testis (“a witness”) +‎ -o.

testor (present infinitive testārī, perfect active testātus sum); first conjugation, deponent

to be witness, testify, attest
to summon as a witness, call to witness, invoke, entreat, swear by, appeal to
- 29 BCE – 19 BCE, Virgil, Aeneid 4.492–493:
  “Testor, cāra, deōs et tē, germāna, tuumque
  dulce caput, magicās invītam accingier artēs.”
  “I call to witness the gods, and you, dear sister, and your sweet life: reluctant to arm magical arts.”
to make a will

Conjugation of testor (first conjugation, deponent)

indicative		singular				plural
indicative		first	second		third	first	second		third
active	present	testor	testāris, testāre		testātur	testāmur	testāminī		testantur
	imperfect	testābar	testābāris, testābāre		testābātur	testābāmur	testābāminī		testābantur
	future	testābor	testāberis, testābere		testābitur	testābimur	testābiminī		testābuntur
	perfect	testātus + present active indicative of sum
	pluperfect	testātus + imperfect active indicative of sum
	future perfect	testātus + future active indicative of sum
subjunctive		singular				plural
subjunctive		first	second		third	first	second		third
active	present	tester	testēris, testēre		testētur	testēmur	testēminī		testentur
	imperfect	testārer	testārēris, testārēre		testārētur	testārēmur	testārēminī		testārentur
	perfect	testātus + present active subjunctive of sum
	pluperfect	testātus + imperfect active subjunctive of sum
imperative		singular				plural
imperative		first	second		third	first	second		third
active	present	—	testāre		—	—	testāminī		—
active	future	—	testātor		testātor	—	—		testantor
non-finite forms		infinitive				participle
non-finite forms		active		passive		active		passive
present		testārī		—		testāns		—
future		testātūrum esse		—		testātūrus		testandus
perfect		testātum esse		—		testātus		—
future perfect		testātum fore		—		—		—
perfect potential		testātūrum fuisse		—		—		—
verbal nouns		gerund					supine
		genitive	dative		accusative	ablative	accusative		ablative
		testandī	testandō		testandum	testandō	testātum		testātū

“testor”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
“testor”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
"testor", in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
testor in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.
Carl Meißner, Henry William Auden (1894) Latin Phrase-Book‎, London: Macmillan and Co.
- to call the gods to witness: testari deos (Sull. 31. 86)
- this shows, proves..: testis est, testatur, declarat
William Dwight Whitney, Benjamin E Smith, editors (1911), “testament”, in The Century Dictionary , New York, N.Y.: The Century Co., →OCLC.