When were the Old Testament and New Testament completed?

Answer 1

Here is a Jewish answer concerning the Tanakh (sometimes called the Old Testament):

Jewish tradition states that from the time of the First Destruction, God's presence was no longer felt as clearly as before (see Deuteronomy 31:17-18). In addition, exile is not conducive to prophecy (Mechilta, parshat Bo). At that time, the last of the prophets realized that prophecy would soon cease; and that the tribulations of the diaspora from the First Destruction onwards, made it imperative to seal the canon of the Tanakh (Hebrew Bible). The Sages of the time, including the last living prophets, convened a special synod for a couple of decades, which was called the Men of the Great Assembly (Mishna, Avot ch.1). This group, who functioned some 2360 years ago, composed the blessings and the basic prayers of the siddur (prayerbook) and the early portions of the Passover Haggadah, made many of the Rabbinical decrees, and (most importantly) sealed the canon of the Tanakh. It was they, for example, who set the twelve Minor Prophets as (halakhically) a single book, and who set the books of the Tanakh in their traditional order (see Talmud, Bava Batra 14b). It was the Men of the Great Assembly whom Esther had to approach when she felt that the Divinely inspired Scroll of Esther should be included in the canon (see Talmud, Megilla 7a).