Caesar's will was read publicly, so unless all of our sources, including Cicero, are lying through their teeth the will as it existed in March of 44 did in fact name Octavian. If Octavian was not named in the will why would Antony have gone to such lengths to prevent him from inheriting the money legally owed him by claiming the will was a forgery?

To my knowledge, there is no dispute over whether or not Octavian was named in Caesar's will, and certainly the fact itself was not outrageous given that the two men were related by blood. It's therefore likely that, in the time that Octavian spent with Caesar prior to the great man's death, he had impressed his Great-Uncle enough to consider him a worthy, Caesarian-blooded heir.

Here is a link to a Reddit post some time ago which will provide a more complete answer from /u/XenophonTheAthenian : https://www.reddit.com/r/AskHistorians/comments/2fcsca/was_is_possible_julius_caesars_will_was_forged_by/