The R&B singer Cassie could testify as soon as Tuesday in Sean “Diddy” Combs’ sex trafficking trial, as the Bad Boy Records founder faces charges that he orchestrated a deviant empire of exploitation that forced women into drugged-up sex parties called “freak-offs.” Testimony in the trial began Monday. Prosecutors told jurors that, for years, Combs used his status as a powerful executive to coerce women into abusive sexual encounters and became violent if they refused.