Basically, the acid test for different Scripture being added to the Bible consisted of 15 criteria:
1) Quotations: A major argument for verifying the authenticity of scripture through the years has involved examining which books were quoted by the canonical books. For example, some will argue that since none of the books of the Apocrypha are quoted in our Bible, then that serves as proof that they do not belong in our Bible.
2) Literature: Another closely related argument says that we need to study what other non-canonical literature claims about the Canon. For example, the famous Jewish historian, Josephus, claims that the real Old Testament is the 22-book Jewish Old Testament like our 39-book Old Testament. This argument gains credibility because of the testimony of men who lived so close to Old Testament times.
3) Divine Inspiration: Some scholars believe that no other books claim to be divinely inspired as they believe the Old Testament does, by 2 Timothy 3:16.
4) Prophets: Scripture can only be recorded through the divine revelation from God. Since there were no prophets during the period of the Apocrypha, how could it be divinely inspired?
5) Errors: Many scholars have rejected the Apocrypha on the basis of the errors and contradictions found within it. In some cases, scholars have reason to believe that some of the moral and spiritual discrepancies are false doctrine rather than translation errors. Some even cite what they call absurdities, or passages that are completely silly, and in no way could belong in the Bible.
6) Style: Scholars also feel that they can identify canonical books by their style.
7) Apostolic Authority: The most important criterion for the books of the New Testament was Apostolic Authority. This meant that a canonical book had to have been written by someone with the Gift of Apostle. This was sometimes difficult to verify because some of the books did not identify within themselves who the author was, and others were believed to be forgeries.
8) Read in the churches: Another important test included verifying that each book had been read in the first century churches. Obviously, this restriction also makes it necessary that the books were completed before the end of the first century.
9) Quoted by leaders: The books had to have been quoted by early church leaders of the first century, in their writings. This is closely associated with 2) under Old Testament.
10) Rule of Faith: The New Testament books had to be consistent with the Rule of Faith, or what the Apostles had orally taught.
11) The Holy Spirit: As proof of divine revelation, the church fathers had to be convinced that each book was written under the guidance of the Holy Spirit.
12) Agreement: There had to be general agreement of the church fathers that each book was canonical.
13) Quotations: The books were given credibility when they were proven to have quoted other canonical books, as well as when other books quoted them as being scripture. This is again like 1) and 2) under Old Testament.
14) Claim Divine Inspiration: Church fathers said that each book had to claim divine inspiration, like 3) under Old Testament.
15) Edification: The books had to edify the church.
For more details, please see the following articles on my website:
https://christiandataresources.com/basicbibledoctrine.htm#thebibleitself
https://christiandataresources.com/canon.htm
https://christiandataresources.com/ph01-01_introtophilippians.htm#historical
I hope this helps.
Thanks,
Owen