My lawyer tried to prepare me for the same thing: if we ask for testing, you'll probably have to do the same. I felt, and still do, the same indignation, disbelief, almost a sense of betrayal. I am NOT the one with a problem. I hadn't had a drink in years, because just the sound of a bottle opening made me nauseous and scared. I wasn't the one stumbling back to the bedroom to berate, intimidate, torture his wife... And then the realization set in that I had and have nothing to hide. (Stilllllll.... *sigh*)
The only additional advice I have would be these 2 pieces:
Tell the cold, hard truth. Hide nothing. Even if it doesn't paint you in the most flattering light. And,
When dealing with an abusive partner, do not sugar coat anything when asked to explain why you felt you and the children were/are in danger. Do not use euphemisms; the court will most likely do that for the transcript any way. Do not minimize. Lay it out, flat, unquestioned, factual. Doing so is not getting on a high horse; it is not trying to denigrate the STX partner. It is giving the courts all the details they need in order to weigh the case.
I struggled with letting go of my need to protect my AXH, which he had ingrained in me over the years. That habit made presenting why DS and I both needed some level of protection from AXH very difficult.