Towards the end of Fantastic Beasts and Where to Find Them there is a scene where Percival Graves, having previously pretended to befriend Credence Barebone with the promise of giving him magical teaching, apparently finds out that Credence is nothing but a squib and says that he is done with him. Seconds later Credence reveals himself as an Obscurial and transforms into an Obscurus. Seeing that he must be a powerful wizard after all, Graves then quickly but unsuccessfully reverts to trying to persuade Credence to accept him as a mentor.
While it is understandable that Graves would lose interest in Credence once the latter seemed no longer to be of use to him, his decision to taunt Credence with being a squib seems surprisingly imprudent. Even if Credence had truly been a squib, publicly dumping him like that converted a loyal henchman into an enemy just when Graves was most likely to need help. In other respects Graves showed a self-disciplined ability to stick to a role.
There would seem to be two most likely explanations for Graves taunting Credence. The first possibility is that because
Graves is really Gellert Grindelwald, his fanatical hatred of all who fail to be proper wizards overcame his common sense.
The second possibility is that he already knew that Credence was an Obscurial and taunted him with being a squib with the specific purpose of of provoking him to transform. That would be in line with his intention of provoking war between the wizards and the No-maj world. On the other hand, it would be a very dangerous strategy to infuriate someone who must be a very powerful wizard to have survived for so long as an Obscurial.
So did Graves know that Credence was the Obscurial before Credence showed himself, or not?