Do my parents have a right to force me to take a paternity test?

My parents' marriage has always been rocky, with doubts about my mother's faithfulness pervading their relationship despite the fact that her infidelity has never been proven. About a year ago, my parents approached me out of the blue about taking a paternity test due to my father's doubt that I am his biological daughter. Given their unhealthy, abusive past, I was immediately concerned about opening an old wound for my father and endangering my mother with this dangerous "evidence." So I agreed to take the test only if my father would be willing to forgive my mom for either result and get counseling for past pains. He was infuriated by this and refused to agree to forgive mom or address his anger. He claims that he "deserves to know the truth" and that I am unfairly torturing him by not taking the test. I do not feel it is my responsibility or obligation to take a paternity test that would contribute nothing to me, but could result in more abuse and resentment toward my mother. At age 33, I could care less about the test results as I am a grown adult who will always relate to my dad as my only father, for better or for worse. I was secure in my decision until several weeks ago when I received a letter from my parents threatening legal action if I do not take the paternity test. I am unsure what the law says on this matter, but I do not trust the courts to act rationally (especially because my mother works for a law firm and has some weight to throw around here). I am now uncertain how to balance protecting myself against protecting them from each other and from additional pain. I have consulted other trusted family members on what to do and they have urged me to hold out on taking the test. What should I do?