Another big day is in the books for the Diddy sex trafficking trial … and today was all about Cassie Ventura‘s testimony as the prosecution’s star witness.

Cassie took the stand and testified about freak-offs, Diddy’s violent temper, his affection for baby oil and how he made her feel objectified by men … namely, by urinating in her mouth so much she started choking.

The singer’s lawyer, Douglas Wigdor, applauded Cassie for sharing her story when our photog got him outside the courthouse … and he told us she’s likely to be on the stand all day Wednesday, answering questions from prosecutors and being cross-examined by Diddy’s legal team.

Cassie talked about her first freak-off with Diddy and a male escort … and got emotional during her testimony, telling the jury the freak-offs felt like a job. She said she told Diddy she didn’t want to participate but went along with it because she didn’t want to upset him or make him angry.

She also told the jury about physical abuse she suffered at Diddy’s hand … and about the time he beat her up in the hallway of a Los Angeles hotel when she left a freak-off before it was supposed to be over, an incident that was caught on camera.

Diddy stared at Cassie as she entered the courtroom Tuesday morning, but she never looked his way … and he watched the jury as she shared her testimony. Cassie’s husband, Alex Fine, was in the gallery to support her.