Stephen De Young (Eastern Orthodox) defends the messianic prophecy in Testament of Joseph 19 being original and not later Christian interpolations.
Stephen De Young, Apocrypha: An Introduction to Extra-Biblical Literature (Chesterton, IN: Ancient Faith Publishing, 2023), 152-54
Messianic Prophecies in Two Versions
Joseph’s story in the Book of Genesis surrounds divinely inspired dreams and their interpretation. The Testament of Joseph ends with his final dream and his interpretation of it. Two versions exist: one found in the Aramaic and the other in Greek. The Greek version of the dream and its interpretation is much shorter, but in some ways more on the nose regarding its messianic prophecies and the Person of Jesus Christ. Thus many scholars think the Greek reflects a post-Christian version of the Jewish text. This supposition raises may questions as it answers, however. There is no clear reason why Christians would omit most of the missing material, which surrounds the history of Judea form the exile to the time of its writing in the Hasmonean period. The Greek texts of the other testaments do not omit similar material. The small details in the messianic portion of the dream in Greek are precisely that: small details. The substance of the messianic prophecy is the same in both.
The Aramaic section omitted in the Greek describes this historical era of Judea, from exile to the Hasmonean period, in a manner similar to the animal apocalypse or Daniel’s vision of the beasts. Animals represent Israelite tribes and nations; horns represent their kings. Following this narration, which constitutes the entire dream in the Greek is a clear prophecy of the coming Messiah, who is a lamb born of a virgin form the tribe of Judah. While modern scholars may find this to be too accurate to be pre-Christian, the wording here in Aramaic or Greek is close though to that of Isaiah 7 that the prophecy is clearly derivative of that found in the Hebrew Bible.
A variety of creatures attack this lamb—not the animals that represented the nations, but reptiles and creeping things—and he defeats them. The lamb represents the salvation of Israel and all the nations, if the people remain true to Levi and Judah. The phrasing of the Greek of Testament of Joseph 19:11, which refers to the Messiah as “the Lamb of God who will take away the sin of the world,” seems an obvious interpolation to many scholars. But when St. John the Forerunner identifies Christ as this figure in John 1:29, the words are a symbolic means used to identify the Messiah. It seems, if anything, more likely that St. John was appealing to the preexisting symbolism to identify Jesus as the Messiah than that St. John here was inventing an unknown image to communicate cryptically with his own followers. Nothing in either version of the Testament of Joseph would require it to be a post-Christian text. Non-Christian Judeans of the early Christian centuries did not disagree with Christians about the coming of a Messiah or the prophecies concerning Him; they disagreed with the Christian claim that Jesus of Nazareth was that figure.