What is the test for a successful claim of ineffective assistance of counsel?

Generally, a successful claim of ineffective assistance of counsel includes two elements; the defendant must show trial counsel's actions fell below professional norms and that it is reasonably probable that a better result would have been obtained had counsel acted according to professional norms. (See People v. Ledesma (1987) 43 Cal.3d 171, 215-218.) But in determining prejudice, "there is no way to ever define just what quantum of evidence is necessary to convince a jury beyond a reasonable doubt of a defendant's guilt." (People v. Accardy (1960) 184 Cal.App.2d 1, 4.) To obtain a better result, a defense counsel merely needs to raise a reasonable doubt in the mind of one juror. (See People v. Soojian (2010) 190 Cal.App.4th 491, 518-521; Wiggins v. Smith (2003) 539 U.S. 510, 537 [156 L.Ed.2d 471, 495].)