Johnson, Aaron, and Jeremy Schott, eds. 2013. Eusebius of Caesarea: Tradition and Innovations. Hellenic Studies Series 60. Washington, DC: Center for Hellenic Studies. http://nrs.harvard.edu/urn-3:hul.ebook:CHS_JohnsonA_SchottJ_eds.Eusebius_of_Caesarea.2013.
5. A Eusebian Reading of the Testimonium Flavianum
Eusebius then assures his readers: “Such was his speech to those present. The author of the present work was given this information shortly afterwards by those who personally heard his words” (Eusebius Life 2.5.5). 
If Cameron and Hall are correct, Eusebius apparently provided his own allegedly outside witness to the truth of Christianity. Might there be other cases where Eusebius has employed this technique of prosōpopoeia, “face-making” (or “character-crafting”), to further his own argument in the voice of another? 
Meier thus posits that Josephus deliberately crafted an ambiguous text so that we cannot be sure what he means by it.
Eusebius not only accepts the Testimonium’s claim that Jesus won over many Gentiles, but exaggerates the number—“many myriads”—and claims that this is the testimony of the evangelists as well. Nor is this the only context in which Eusebius claims that Jesus attracted Gentiles during his ministry. In Demonstration IV, 10, Eusebius lists among other deeds of Jesus during his incarnation: “He set all that came to Him free from age-long superstition and the fears of polytheistic error” (4.10.14).  He is presumably not referring to Jews. In Demonstration 8.2, Eusebius claims that “by teaching and miracles He revealed the powers of His Godhead to all equally whether Greeks or Jews” (8.2.109).  In the Ecclesiastical History, Eusebius introduces the story of the conversion of King Abgar and the city of Edessa by saying: “The divinity of our Lord and Saviour Jesus Christ became famous among all men because of his wonder-working power, and led to him myriads even of those who in foreign lands were far remote from Judea, in the hope of healing from diseases and from all kinds of suffering” (1.13.1).  In Book VII, he also tells of a statue of Jesus in Caesarea Philippi erected to honor Jesus’ healing of the woman with a flow of blood. Eusebius comments: “And it is not at at all surprising that those Gentiles, who long ago received benefits from our Savior, should have made these things” (7.18.4). Whatever we may suppose as to whether Jesus attracted Gentiles during his ministry, we should allow that Eusebius thought he did. Further, Eusebius devotes the entirety of Book II of the Demonstration to answering the charge that the Christ was promised to the Jews. Eusebius argues, to the contrary, that the hope of the Christ was promised equally to the Jews and Gentiles and that the Christian church contains both Gentiles and the remnant of the Jews.
I have followed Meier here in translating the initial genitive absolute as a concessive clause.  On Meier’s reading, the second half of the Testimonium suggests that the author of the text is surprised that Jesus’ following continued after Jesus’ death. Meier says:
Meier is again quite correct in understanding that the text communicates that the continuance of Christianity after Jesus’ death is surprising. But if we read the text as it stands and include the claim that Jesus appeared to the disciples alive again, we have an explanation for this surprising event. Moreover, this is a key argument that Eusebius makes for the reliability of the disciples’ report of the resurrection earlier in the same chapter of the Demonstration in which he produces the Testimonium. Eusebius, like the Testimonium, finds the behavior of the disciples surprising. He says: “surely they had all seen the end of their teacher, and the death to which He came. Why then after seeing His miserable end did they stand their ground?” (3.5.39); and again: “I ask you how these pupils of a base and shifty master, who had seen His end, discussed with one another how they should invent a story about Him which would hang together?” (3.5.113).  Eusebius’ argument in this part of the chapter is that the disciples’ continued adherence to Jesus’ teachings and the subsequent success of their mission is inexplicable apart from the reality of the resurrection appearances, which demonstrated the truth of what Jesus taught. Later in the Demonstration, Eusebius enumerates the reasons for the resurrection itself and ranks as number five Christ’s need to give his disciples ocular proof of life after death so that they would have the courage to preach his message to all nations (Demonstration 4.12). In his later work In Praise of Constantine, Eusebius ranks this reason for the resurrection first (Tricennial Orations: On Christ’s Sepulcher 15.7).