What is the legal test for deficient counsel in a criminal case?

"deficient" because his "representation fell below an objective standard of reasonableness . . . under prevailing professional norms." [Citations.] Second, he must also show prejudice flowing from counsel's performance or lack thereof. [Citation.] Prejudice is shown when there is a "reasonable probability that, but for counsel's unprofessional errors, the result of the proceeding would have been different. A reasonable probability is a probability sufficient to undermine confidence in the outcome."'" [Citation.] [] Reviewing courts defer to counsel's reasonable tactical decisions in examining a claim of ineffective assistance of counsel [citation], and there is a "strong presumption that counsel's conduct falls within the wide range of reasonable professional assistance." [Citation.] Defendant's burden is difficult to carry on direct appeal, as we have observed: "'Reviewing courts will reverse convictions [on direct appeal] on the ground of inadequate counsel only if the record on appeal affirmatively discloses that counsel had no rational tactical purpose for [his or her] act or omission.'" [Citation.]' [Citation.] If the record on appeal '"'sheds no light on why counsel acted or failed to act in the manner challenged[,] unless counsel was asked for an explanation and failed to provide one, or unless there simply could be no satisfactory explanation,' the claim on appeal must be rejected,"' and the 'claim of ineffective assistance in such a case is more appropriately decided in a habeas corpus proceeding.' [Citation.]" (People v. Vines, supra, 51 Cal.4th at pp. 875-876.)

CALCRIM No. 1403, as presumably would have been given had defense counsel requested it below, provides:

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"You may consider evidence of gang activity only for the limited purpose of deciding whether: The defendant acted with the intent, purpose, and knowledge that are required to prove the gang-related . . . enhancement[s] . . . charged; or the defendant had a motive to commit the crime[s] charged. . . . You may not consider this evidence for any other purpose. You may not conclude from this evidence that the defendant is a person of bad character or that [he] has a disposition to commit crime." On request, the court must give a limiting instruction when evidence of gang activity has been admitted. However, there is no sua sponte duty to do so. (People v. Hernandez (2004) 33 Cal.4th 1040, 1051-1052.)