What is the test for ineffective assistance of counsel?

While contending that his conviction should be reversed due to the admission of excessive gang-related evidence, appellant at the same time complains that his trial counsel rendered ineffective assistance by agreeing to enter into the gang stipulation. "To establish entitlement to relief for ineffective assistance of counsel the burden is on the defendant to show (1) trial counsel failed to act in the manner to be expected of reasonably competent attorneys acting as diligent advocates and (2) it is reasonably probable that a more favorable determination would have resulted in the absence of counsel's failings. [Citations.]" (People v. Lewis (1990) 50 Cal.3d 262, 288.) Where the record affirmatively discloses a reasonable tactical basis for a decision made by a criminal defendant's trial counsel, we defer to that decision, and apply a strong presumption that counsel's conduct falls within the wide range of reasonable professional assistance. (People v. Stanley (2006) 39 Cal.4th 913, 954.)