Questions & Answers about Testis iurat se verum dicere.
Because testis is the subject of iurat.
- testis = the witness
- iurat = swears
In Latin, the subject of a finite verb is normally in the nominative case, just as in English the subject is the one doing the action.
Testis is a third-declension noun. Its basic dictionary form is:
- testis, testis (m./f.) = witness
A learner might expect a nominative ending like -us or -a, but many third-declension nouns have other endings, and -is is very common there.
Iurat is:
- third person singular
- present tense
- active voice
- indicative mood
It means he/she swears or the witness swears.
Why singular? Because the subject testis is singular.