What is the test for establishing a prima facie case of legal malpractice or negligence?

To establish a prima facie case of legal malpractice or negligence, the client must plead and prove facts tending to show that the law firm: 1) failed to exercise that degree of care, skill, and diligence commonly possessed and exercised by an ordinary member of the legal community, 2) that such negligence was the proximate cause of the actual damages sustained by the plaintiff and, 3) that "but for" the defendant's negligence, the plaintiff would have been successful in the underlying matter (Laventure v. Galeno, 307 AD2d 255 [1st Dept. 2003]; Wexler v. Shea & Gould, 211 AD2d 450, 621 NYS2d 858 [1sl Dept. 1995]).