Sergeant 'intimidated' rookie doing RBT

A rookie police officer felt intimidated by an off-duty senior colleague who "came across as a little bit aggressive" when she refused to be randomly breath tested by him, a Sydney court has heard.

"I was taught to respect authority and she's a sergeant of police and I'm a probationary constable with a year's experience", the now constable Tugcan Sackesen told the Downing Centre District Court on Thursday.

Sarah Louise Johnston, 50, is on trial for using her rank and authority to avoid a breath test with intent to pervert the course of justice at North Sydney on January 8, 2016.

The court previously heard she'd had at least one schooner of beer while celebrating the new year with colleagues from North Sydney Police Station at two nearby pubs.

Johnston was driving home to the Central Coast when she was pulled over at a random breath testing site on the Pacific Highway at Crows Nest.

Two junior officers conducting the RBTs - Constable Cameron Brooks and Mr Sackesen - immediately recognised her.

On Thursday Const Sackesen told the court Johnston first pulled up alongside Const Brooks but she rolled forward towards him before Const Brooks could breath test her.

"Hi sergeant you've just been stopped for a random breath test," Mr Sackesen told her.

"You're not going to breath test me are you?" she replied, he said.

"Yes sergeant I am," he said.

She allegedly said: "No because that would be a conflict of interest."

"Imagine if I blew over, which I won't, because I'm not."

Johnston told him it would put him in an "awkward situation", he said.

Mr Sackesen told the court Johnston was "confident and stern" and "came across as a little bit aggressive to the point I believed she was telling the truth and I was wrong".

He said it made him doubt his knowledge and "intimidated me a little bit".

Johnston drove off without having been tested, he said.

The trial continues before Judge Christopher Hoy.