Donald Trump has vowed to testify on Monday in writer E. Jean Carroll’s defamation case in New York, but one MSNBC legal analyst thinks it is a fake-out. Attorney Lisa Rubin posted a prediction on Saturday, and used her knowledge of the legal system to bring it home. “Any former trial lawyer can tell you that witness prep is essential. And with a plaintiff, defendant, or C-suite exec of either, that prep begins well in advance of trial & often involves faux cross. And that brings me to everyone’s fave defamation defendant, Donald Trump,” Rubin wrote, adding that the former president “has a jam…