What is the legal test for ineffective assistance of counsel?

" 'In order to establish a claim of ineffective assistance of counsel, defendant bears the burden of demonstrating, first, that counsel's performance was deficient because it "fell below an objective standard of reasonableness [] . . . under prevailing professional norms." [Citations.] Unless a defendant establishes the contrary, we shall presume that "counsel's performance fell within the wide range of professional competence and that counsel's actions and inactions can be explained as a matter of sound trial strategy." [Citation.] . . . If a defendant meets the burden of establishing that counsel's performance was deficient, he or she also must show that counsel's deficiencies resulted in prejudice, that is, a "reasonable probability that, but for counsel's unprofessional errors, the result of the proceeding would have been different." [Citation.]' [Citation.]" (People v. Lopez (2008) 42 Cal.4th 960, 966; see Strickland v. Washington (1984) 466 U.S. 668.)