Historically Christianaity clearly is founded by Jesus through the church instrument of the Apostles. The Apostles wrote in written form the word of God. Thus we have the New Testament.
John wrote in the gospel, this is a disciple bearing witness to these things. We also confirm that each testamony was given by at least three each time. This would ensample the evident idenity of God's intervention for that which was written. The New Testament grew organically by the church under the inspiration of the Holy Spirit..
Noting that Christianity was not founded by the New Testament but rather by the Apostles instructions which is the summary of the New Testament.
The discoverage of the written inspirition of God is known as the Muratorian Canon which was dated 190, and discovered in 1740. By the end of the 4th century under the influence of St Augustine bishops met at the councils of Hippo and Carthage. They, at that time, accepted books known today as the New Testament. This further was worked by Martin Luther which brought about changes that eliminated some of the original books. After which when the council of Trent decreed on the matter in the sixteenth century it merely formalized what had been accepted for well over thirteen centuries.